Role of c-jun expression increased by heat shock- and ceramide-activated caspase-3 in HL-60 cell apoptosis. Possible involvement of ceramide in heat shock-induced apoptosis

GEO dataset mining analysis reveals novel Staphylococcus aureus virulence gene regulatory networks and diagnostic targets in mice

Staphylococcus (S.) aureus infection is a serious, worldwide health concern, particularly in many communities and hospitals. Understanding the S. aureus pathogenetic regulatory network will provide significant insights into diagnostic target screening to improve clinical treatment of diseases caused by S. aureus. We screened differentially expressed genes between normal mice and S. aureus-infected mice. We used the Gene Expression Omnibus (GEO) DataSets database for functional analysis (GO-analysis) and the DAVID and KEGG databases for signaling pathway analyses. We next integrated the gene and pathway analyses with Transcriptional Regulatory Element Database (TRED) to build an antimicrobial resistance gene regulatory network of S. aureus. We performed association analysis of network genes and diseases using DAVID online annotation tools. We identified a total of 437 virulence genes and 15 transcription factors (TFs), as well as 444 corresponding target genes, in the S. aureus TF regulatory network. We screened seven key network nodes (Met, Mmp13, Il12b, Il4, Tnf, Ptgs2, and Ctsl), four key transcription factors (Jun, C3, Spil, and Il6) and an important signaling pathway (TNF). We hypothesized that the cytokine activity and growth factor activity of S. aureus are combinatorically cross-regulated by Met, Mmp13, Il12b, Il4, Tnf, Ptgs2, and Ctsl genes, the TFs Jun, C3, Spi1, and Il6, as well as the immune response, cellular response to lipopolysaccharide, and inflammatory response. Our study provides information and reference values for the molecular understanding of the S. aureus pathogenetic gene regulatory network.

Nuclear Ceramide Is Associated with Ataxia Telangiectasia Mutated Activation in the Neocarzinostatin-Induced Apoptosis of Lymphoblastoid Cells

Ceramide is a bioactive sphingolipid that mediates ionizing radiation- and chemotherapy-induced apoptosis. Neocarzinostatin (NCS) is a genotoxic anti-cancer drug that induces apoptosis in response to DNA double-strand breaks (DSBs) through ataxia telangiectasia mutated (ATM) activation. However, the involvement of ceramide in NCS-evoked nuclear events such as DSB-activated ATM has not been clarified. Here, we found that nuclear ceramide increased by NCS-mediated apoptosis through the enhanced assembly of ATM and the meiotic recombination 11/double-strand break repair/Nijmengen breakage syndrome 1 (MRN) complex proteins in human lymphoblastoid L-39 cells. NCS induced an increase of ceramide production through activation of neutral sphingomyelinase (nSMase) and suppression of sphingomyelin synthase (SMS) upstream of DSB-mediated ATM activation. In ATM-deficient lymphoblastoid AT-59 cells compared with L-39 cells, NCS treatment showed a decrease of apoptosis even though ceramide increase and DSBs were observed. Expression of wild-type ATM, but not the kinase-dead mutant ATM, in AT-59 cells increased NCS-induced apoptosis despite similar ceramide accumulation. Interestingly, NCS increased ceramide content in the nucleus through nSMase activation and SMS suppression and promoted colocalization of ceramide with phosphorylated ATM and foci of MRN complex. Inhibition of ceramide generation by the overexpression of SMS suppressed NCS-induced apoptosis through the inhibition of ATM activation and assembly of the MRN complex. In addition, inhibition of ceramide increased by the nSMase inhibitor GW4869 prevented NCS-mediated activation of the ATM. Therefore, our findings suggest the involvement of the nuclear ceramide with ATM activation in NCS-mediated apoptosis. SIGNIFICANCE STATEMENT: This study demonstrates that regulation of ceramide with neutral sphingomyelinase and sphingomyelin synthase in the nucleus in double-strand break-mimetic agent neocarzinostatin (NCS)-induced apoptosis. This study also showed that ceramide increase in the nucleus plays a role in NCS-induced apoptosis through activation of the ataxia telangiectasia mutated/meiotic recombination 11/double-strand break repair/Nijmengen breakage syndrome 1 complex in human lymphoblastoid cells.

Heat stress impairs oocyte maturation through ceramide-mediated apoptosis in pigs

Heat stress (HS) is an emerging issue that greatly impairs the reproductive performance of animals and humans. In particular, disruption of oocyte maturation due to HS is considered a major cause of impaired reproductive performance. HS is known to induce ceramide generation, which causes reactive oxygen species (ROS) production and mitochondrial dysfunction, thereby inducing apoptosis. Therefore, we investigated whether inhibition of ceramide generation ameliorates HS-induced apoptosis in porcine cumulus-oocyte complexes (COCs) using specific inhibitors of the de novo (fumonisin B1, FB1) and hydrolytic pathways (desipramine, Des) of ceramide formation. We investigated the effects of FB1 and Des supplementation under HS conditions (41.5 °C for 44 h) on in vitro maturation (IVM) of porcine COCs. After IVM, HS significantly reduced proportion of COCs exhibiting fully expanded cumulus cells and the rate of metaphase II in oocytes. After parthenogenetic activation (PA), HS significantly reduced the rates of cleavage and blastocyst formation with a lower total cell number and a higher percentage of apoptosis in blastocysts. However, FB1 or Des supplementation under HS avoided detrimental effects of HS on expansion of cumulus cells, nuclear maturation of oocytes, and embryonic development after PA including the rates of cleavage and blastocyst formation, total cell number, and the percentage of apoptosis in blastocysts. Furthermore, FB1 or Des addition under HS, compared with HS alone, significantly decreased ceramide generation, ROS production, cytochrome C expression, and apoptosis and increased mitochondrial membrane potential in COCs, reaching levels comparable with those of the control. Taken together, our results indicate that HS impaired oocyte maturation through ceramide-mediated apoptosis.

The dynamics and role of sphingolipids in eukaryotic organisms upon thermal adaptation

All living beings have an optimal temperature for growth and survival. With the advancement of global warming, the search for understanding adaptive processes to climate changes has gained prominence. In this context, all living beings monitor the external temperature and develop adaptive responses to thermal variations. These responses ultimately change the functioning of the cell and affect the most diverse structures and processes. One of the first structures to detect thermal variations is the plasma membrane, whose constitution allows triggering of intracellular signals that assist in the response to temperature stress. Although studies on this topic have been conducted, the underlying mechanisms of recognizing thermal changes and modifying cellular functioning to adapt to this condition are not fully understood. Recently, many reports have indicated the participation of sphingolipids (SLs), major components of the plasma membrane, in the regulation of the thermal stress response. SLs can structurally reinforce the membrane or/and send signals intracellularly to control numerous cellular processes, such as apoptosis, cytoskeleton polarization, cell cycle arresting and fungal virulence. In this review, we discuss how SLs synthesis changes during both heat and cold stresses, focusing on fungi, plants, animals and human cells. The role of lysophospholipids is also discussed.

Reduction of Thermotolerance by Heat Shock Protein 90 Inhibitors in Murine Erythroleukemia Cells

Cells induce heat shock proteins (HSPs) against various stress. However, murine erythroleukemia (MEL) cells do not express HSP72, a heat-inducible member of HSP70 family. So, it is of interest to examine how MEL cells respond to heat stress (44°C, 30 min). Heat stress-induced apoptosis was suppressed by pretreatment of heat shock (44°C, 10 min). Such suppressive effects were maximal at 6 h after heat shock and remained up to 12 h. Interestingly, such effects of heat shock were abrogated by specific inhibitors of HSP90 such as 17-allylamino-17-demethoxygeldanamycin (17-AAG) and novobiocin. From flow cytometric analysis, it was found that MEL cells arrest in G₂ phase at 6 h after heat shock, but restore original cell cycle at 12 h. High expression level of HSP90 was maintained before and after heat shock. Phosphorylation of HSP90α was observed in apoptotic cells induced by heat stress, but inhibited by pretreatment of heat shock. Such inhibition was abrogated by 17-AAG. Moreover, c-Jun NH₂-terminal kinase (JNK) was activated in heat stress-induced apoptotic cells. Taken together, these results suggest that HSP90α in MEL cells plays an important role in the thermotolerance, i.e., suppression of heat stress-induced apoptosis by heat shock.

Tumor suppressive functions of ceramide: evidence and mechanisms

Studies over the past two decades have identified ceramide as a multifunctional central molecule in the sphingolipid biosynthetic pathway. Given its diverse tumor suppressive activities, molecular understanding of ceramide action will produce fundamental insights into processes that limit tumorigenesis and may identify key molecular targets for therapeutic intervention. Ceramide can be activated by a diverse array of stresses such as heat shock, genotoxic damage, oxidative stress and anticancer drugs. Ceramide triggers a variety of tumor suppressive and anti-proliferative cellular programs such as apoptosis, autophagy, senescence, and necroptosis by activating or repressing key effector molecules. Defects in ceramide generation and metabolism in cancer contribute to tumor cell survival and resistance to chemotherapy. The potent and versatile anticancer activity profile of ceramide has motivated drug development efforts to (re-)activate ceramide in established tumors. This review focuses on our current understanding of the tumor suppressive functions of ceramide and highlights the potential downstream targets of ceramide which are involved in its tumor suppressive action.

Aaptamines from the marine sponge Aaptos sp. display anticancer activities in human cancer cell lines and modulate AP-1-, NF-κB-, and p53-dependent transcriptional activity in mouse JB6 Cl41 cells

Aaptamine (8,9-dimethoxy-1H-benzo[de][1,6]naphthyridine) is a marine natural compound possessing antioxidative, antimicrobial, antifungal, and antiretroviral activity. Earlier, we have found that aaptamine and its derivatives demonstrate equal anticancer effects against the human germ cell cancer cell lines NT2 and NT2-R and cause some changes in the proteome of these cells. In order to explore further the mechanism of action of aaptamine and its derivatives, we studied the effects of aaptamine (1), demethyl(oxy)aaptamine (2), and isoaaptamine (3) on human cancer cell lines and on AP-1-, NF-κB-, and p53-dependent transcriptional activity in murine JB6 Cl41 cells. We showed that compounds 1–3 demonstrate anticancer activity in THP-1, HeLa, SNU-C4, SK-MEL-28, and MDA-MB-231 human cancer cell lines. Additionally, all compounds were found to prevent EGF-induced neoplastic transformation of murine JB6 Cl41 cells. Nuclear factors AP-1, NF-κB, and p53 are involved in the cellular response to high and nontoxic concentrations of aaptamine alkaloids 1–3. Furthermore, inhibition of EGF-induced JB6 cell transformation, which is exerted by the compounds 1–3 at low nontoxic concentrations of 0.7–2.1 μM, cannot be explained by activation of AP-1 and NF-κB.

Zebrafish neurotoxicity from aphantoxins--cyanobacterial paralytic shellfish poisons (PSPs) from Aphanizomenon flos-aquae DC-1

Aphanizomenon flos-aquae (A. flos-aquae), a cyanobacterium frequently encountered in water blooms worldwide, is source of neurotoxins known as PSPs or aphantoxins that present a major threat to the environment and to human health. Although the molecular mechanism of PSP action is well known, many unresolved questions remain concerning its mechanisms of toxicity. Aphantoxins purified from a natural isolate of A. flos-aquae DC-1 were analyzed by high-performance liquid chromatography (HPLC), the major component toxins were the gonyautoxins1 and 5 (GTX1 and GTX5, 34.04% and 21.28%, respectively) and the neosaxitoxin (neoSTX, 12.77%). The LD50 of the aphantoxin preparation was determined to be 11.33 μg/kg (7.75 μg saxitoxin equivalents (STXeq) per kg) following intraperitoneal injection of zebrafish (Danio rerio). To address the neurotoxicology of the aphantoxin preparation, zebrafish were injected with low and high sublethal doses of A. flos-aquae DC-1 toxins 7.73 and 9.28 μg /kg (5.3 and 6.4 μg STXeq/kg, respectively) and brain tissues were analyzed by electron microscopy and RT-PCR at different timepoints postinjection. Low-dose aphantoxin exposure was associated with chromatin condensation, cell-membrane blebbing, and the appearance of apoptotic bodies. High-dose exposure was associated with cytoplasmic vacuolization, mitochondrial swelling, and expansion of the endoplasmic reticulum. At early timepoints (3 h) many cells exhibited characteristic features of both apoptosis and necrosis. At later timepoints apoptosis appeared to predominate in the low-dose group, whereas necrosis predominated in the high-dose group. RT-PCR revealed that mRNA levels of the apoptosis-related genes encoding p53, Bax, caspase-3, and c-Jun were upregulated after aphantoxin exposure, but there was no evidence of DNA laddering; apoptosis could take place by pathways independent of DNA fragmentation. These results demonstrate that aphantoxin exposure can cause cell death in zebrafish brain tissue, with low doses inducing apoptosis and higher doses inducing necrosis.

The Extracts of Some Marine Invertebrates and Algae Collected off the Coast Waters of Vietnam Induce the Inhibitory Effects on the Activator Protein-1 Transcriptional Activity in JB6 Cl41 Cells

It has previously been shown that inhibition of the transcriptional activity of the oncogenic nuclear factor AP-1 can result in cancer prevention. Marine invertebrates and alga are a rich source of natural compounds that possess various biological activities. The inhibitory effects of the extracts of Vietnamese marine organisms in relation to the AP-1 transcriptional activity were examined by the luciferase method using JB6 Cl41 cells stably expressing a luciferase reporter gene controlled by AP-1 DNA binding sequence. As was found, 71 species of marine sponges out of 148 species studied contain inhibitors of the AP-1 transcriptional activity. Therefore, marine organisms as a source of biologically active compounds have a great potential for isolation of the new cancer preventive compounds that inhibit the oncogenic AP-1 nuclear factor.

Aqueous Extract of Phyllanthus urinaria Induces Apoptosis in Human Cancer Cells

Cell apoptosis is now known to play an important role in the maintenance of cellular homeostasis and anti-carcinogenesis. The anticancer effect of aqueous extract prepared from Phyllanthus urinaria (P. urinaria) was investigated by analyzing its potential to induce apoptosis in human cancer cells. We showed that the aqueous extract of P. urinaria could reduce the viability by inducing the apoptosis in human cancer cells derived from several different origins as demonstrated by morphological changes and DNA fragmentation. Yet, P. urinaria extract exhibited no cytotoxic effect on normal human cells, including vascular endothelial cells and liver cells under the same conditions. It suggests that the aqueous extract of P. urinaria is substantially useful in treating various kinds of human cancer cells without toxic side effect on normal cells.

Curcumin induces the apoptosis of human monocytic leukemia THP-1 cells via the activation of JNK/ERK pathways

BACKGROUND

Curcumin is a principal compound of turmeric, commonly used to treat tumors and other diseases. However, its anti-cancer activity in human acute monocytic leukemia THP-1 cells is not clear. This study aimed to study the anti-cancer effect and action of curcumin on THP-1 cells.

METHODS

THP-1 parental cells and PMA-treated THP-1 cells, were used as in vitro models to evaluate the anti-cancer effect and mechanism of curcumin. Apoptosis and its mechanism were evaluated by WST-1, flow cytometry and Western blotting. MAPK inhibitors were used to further confirm the molecular mechanism of curcumin-induced THP-1 cell apoptosis.

RESULTS

Curcumin induced cell apoptosis of THP-1 cells as shown by cell viability, cell cycle analysis and caspase activity. Curcumin significantly increased the phosphorylation of ERK, JNK and their downstream molecules (c-Jun and Jun B). Inhibitor of JNK and ERK reduced the pro-apoptotic effect of curcumin on THP-1 cells as evidenced by caspase activity and the activation of ERK/JNK/Jun cascades. On the contrary, the pro-apoptotic effect of curcumin was abolished in the differentiated THP-1 cells mediated by PMA.

CONCLUSIONS

This study demonstrates that curcumin can induce the THP-1 cell apoptosis through the activation of JNK/ERK/AP1 pathways. Besides, our data suggest its novel use as an anti-tumor agent in acute monocytic leukemia.

Involvement of the sphingolipid ceramide in heat-shock-induced apoptosis of bovine oocytes

Programmed cell death via the sphingomyelin pathway has been suggested to underlie heat-shock disturbance of oocyte developmental competence. A series of experiments were performed to characterise the role of the sphingolipid ceramide in heat-shock-induced apoptosis, and to determine whether ceramide formation can be regulated. Bovine cumulus–oocyte complexes (COCs) were aspirated from ovaries collected in the cold season (November–April), in vitro-matured, fertilised and cultured for 8 days. Exposure of COCs to heat shock (41°C) during maturation reduced cleavage rate and blastocyst formation relative to the control group (38.5°C). Annexin-V binding (V-FITC assay), which is associated with the early apoptotic event of membrane phosphatidylserine turnover, was higher in oocytes exposed to short-term versus long-term heat shock, suggesting that heat-shock-induced apoptosis involves membrane alterations. Similar to heat exposure, oocyte maturation with C2-ceramide had a dose-dependent deleterious effect on the first cleavages and subsequent embryonic development in association with increased annexin-V binding. Blocking endogenous ceramide generation with fumonisin B1, a specific inhibitor of dihydroceramide synthase (i.e. de novo formation), moderated, to some extent, the effects of heat shock on oocyte developmental competence, suggesting that ceramide plays an important role in heat-shock-induced apoptosis.

PP2A mediated AMPK inhibition promotes HSP70 expression in heat shock response

BACKGROUND

Under stress, AMP-activated protein kinase (AMPK) plays a central role in energy balance, and the heat shock response is a protective mechanism for cell survival. The relationship between AMPK activity and heat shock protein (HSP) expression under stress is unclear.

METHODOLOGY/PRINCIPAL FINDINGS

We found that heat stress induced dephosphorylation of AMPKα subunit (AMPKα) in various cell types from human and rodent. In HepG2 cells, the dephosphorylation of AMPKα under heat stress in turn caused dephosphorylation of acetyl-CoA carboxylase and upregulation of phosphoenolpyruvate carboxykinase, two downstream targets of AMPK, confirming the inhibition of AMPK activity by heat stress. Treatment of HepG2 cells with phosphatase 2A (PP2A) inhibitor okadaic acid or inhibition of PP2A expression by RNA interference efficiently reversed heat stress-induced AMPKα dephosphorylation, suggesting that heat stress inhibited AMPK through activation of PP2A. Heat stress- and other HSP inducer (CdCl(2), celastrol, MG132)-induced HSP70 expression could be inhibited by AICAR, an AMPK specific activator. Inhibition of AMPKα expression by RNA interference reversed the inhibitory effect of AICAR on HSP70 expression under heat stress. These results indicate that AMPK inhibition under stress contribute to HSP70 expression. Mechanistic studies showed that activation of AMPK by AICAR had no effect on heat stress-induced HSF1 nuclear translocation, phosphorylation and binding with heat response element in the promoter region of HSP70 gene, but significantly decreased HSP70 mRNA stability.

CONCLUSIONS/SIGNIFICANCE

These results demonstrate that during heat shock response, PP2A mediated AMPK inhibition upregulates HSP70 expression at least partially through stabilizing its mRNA, which suggests a novel mechanism for HSP induction under stress.

Synthesis and evaluation of sphingosine analogues as inhibitors of sphingosine kinases

Sphingolipid-metabolizing enzymes control the critical balance of the cellular levels of sphingolipids, including the apoptotic inducing ceramide (Cer) and the proliferative inducing sphingosine 1-phosphate (S1P). The production of S1P, catalyzed by the action of sphingosine kinases (SPHKs), is known to be critical for many cellular processes. However, it is suggested that SPHK, and/or its catalytic product S1P, plays critical roles in various diseases including autoimmune diseases, cancer, and allergies. However, there is a great limitation of specific pharmacological inhibitors for SPHKs. In this paper, we describe a novel and stereoselective method of synthesizing SPHKs inhibitors. We generated a number of novel compounds and identified a number of specific inhibitors of human SPHKs. These compounds demonstrated inhibition of SPHKs at micromolar concentrations, making them more potent than dimethylsphingosine (DMS), a well-known inhibitor of SPHKs. In particular, one of the inhibitors was found to be selective toward a particular isoform of SPHK.

Study of heat shock response of human umbilical vein endothelial cells (HUVECs) using cDNA microarray

Genetic response of human umbilical vein cells (HUVECs) to heat shock was studied using gene expression analysis. HUVECs were subjected to heat treatment at 44 degrees C and 55 degrees C for 1 h, respectively. Four hours after the treatment, gene expression of the treated cells and control cells (37 degrees C) were profiled using cDNA microarray. Data were analyzed using bioinformatics tools, and the results were verified by real-time quantitative PCR experiment. It has been shown that a large number of genes were regulated indicating global response to heat treatment at the genetic level.

Gene expression in enhanced apoptosis of human lymphoma U937 cells treated with the combination of different free radical generators and hyperthermia

The effects of various free radicals derived from 6-formylpterin (6-FP), alpha-phenyl-tert-butyl nitrone (PBN) and 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) combined with hyperthermia, on gene expression in similarly enhanced apoptosis of human lymphoma U937 cells were investigated using cDNA microarrays containing approximately 16,600 genes and computational gene expression analysis tools. When the cells were treated for 10 min at 44 degrees C (15% apoptosis level), 39 up-regulated and 3 down-regulated genes were identified. In the up-regulated genes, apoptosis- and unfolded protein response-associated genes were contained. The combined treatment with heat and either chemical enhanced apoptosis level (approximately 30%) and showed a chemical-specific gene expression pattern. Furthermore, the expression levels of selected genes were confirmed by a real-time quantitative PCR. The present results will provide a basis for further understanding the molecular mechanisms in enhancement of heat-induced apoptosis by different intracellular oxidative stress.

c-Jun blocks cell differentiation but not growth inhibition or apoptosis of chronic myelogenous leukemia cells induced by STI571 and by histone deacetylase inhibitors

The constitutively active Bcr-Abl tyrosine kinase plays a crucial role in chronic myelogenous leukemia (CML) pathogenesis. The Bcr-Abl protein induces the upregulation of proto-oncogene c-Jun, which is involved in Bcr-Abl transforming activity in Bcr-Abl positive cells. Recent studies reported that c-Jun inhibited hemoglobin synthesis in human CML cell line K562. However, c-Jun also plays a critical role in cell proliferation and apoptosis. In this study, we investigated the physiological roles of c-Jun in cell proliferation, apoptosis and erythroid differentiation of K562 cells. Firstly, we generated K562 cell lines stably overexpressing c-Jun. These clones have the same proliferation rate as the parental cell line in general culture medium. Endogenous c-Jun expression was analyzed to determine the effective concentration of STI571 for inhibiting Bcr-Abl signaling. Western blots show that STI571 inhibited c-Jun expression in a dose-dependent manner, reaching a maximum inhibition at 1 microM. STI571 could inhibit c-Jun expression in K562 cells, but not in c-Jun-overexpression cells. c-Jun did not alter growth inhibition and apoptotic induction by STI571 treatment, but inhibited STI571-induced erythroid differentiation. Moreover, c-Jun did not alter growth inhibition and apoptotic induction by histone deacetylase (HDAC) inhibitors (apicidin, sodium butyrate, and MS275) treatment, but inhibited HDAC inhibitors-induced erythroid differentiation. These results suggest that c-Jun may modulate anticancer drugs-induced cell differentiation but not growth inhibition and apoptosis in CML cells.

Identification of Mg2+ -dependent neutral sphingomyelinase 1 as a mediator of heat stress-induced ceramide generation and apoptosis

Neutral sphingomyelinases (SMases) are involved in the induction of ceramide-mediated proapoptotic signaling under heat stress conditions. Although ceramide is an important mediator of apoptosis, the neutral SMase that is activated under heat stress has not been identified. In this study, we cloned an Mg(2+)-dependent neutral SMase from a zebrafish embryonic cell cDNA library using an Escherichia coli expression-cloning vector. Screening of the clones using an SMase activity assay with C(6)-7-nitro-2-1,3-benzoxadiazol-4-yl-sphingomyelin as the substrate resulted in the isolation of one neutral SMase cDNA clone. This cDNA encoded a polypeptide of 420 amino acids (putative molecular weight: 46,900) containing two predicted transmembrane domains in its C-terminal region. The cloned neutral SMase 1 acted as a mediator of stress-induced apoptosis. Bacterially expressed recombinant neutral SMase 1 hydrolyzed [choline-methyl-(14)C]sphingomyelin optimally at pH 7.5 in the presence of an Mg(2+) ion. In zebrafish embryonic cells, the endogenous SMase enzyme was localized in the microsomal fraction. In FLAG-tagged SMase-overexpressing cells, neutral SMase 1 colocalized with a Golgi marker in a cytochemical analysis. Inactivation of the enzyme by an antisense phosphorothioate oligonucleotide repressed the induction of ceramide generation, caspase-3 activation, and apoptotic cell death by heat stress. Thus, neutral SMase 1 participates in an inducible ceramide-mediating, proapoptotic signaling pathway that operates in heat-induced apoptosis in zebrafish embryonic cells.

Ceramide inhibits development and cytokinesis and induces apoptosis in preimplantation bovine embryos

Ceramide is a second messenger induced by various cellular insults that plays a regulatory role in apoptosis. The objective of the present study was to determine whether ceramide signaling can occur in the preimplantation embryo by testing (1) effects of ceramide on development, cytokinesis, and apoptosis and (2) whether heat shock, which can induce apoptosis in embryos, causes activation of neutral or acidic sphingomyelinases responsible for generation of ceramide. Treatment of embryos > or =16 cells collected at Day 5 after insemination with 50 microM C(2)-ceramide increased caspase-9 activity and the proportion of blastomeres undergoing apoptosis but did not increase caspase-8 activity. Induction of apoptosis was more extensive when culture with ceramide was for 24 hr than for 9 hr. Ceramide also reduced the proportion of embryos that developed to the blastocyst stage when exposure was for 24 hr. At the two-cell stage, a period in development when apoptosis responses are blocked, culture of embryos with ceramide did not increase caspase-9 activity or the proportion of blastomeres that were apoptotic. However, culture with ceramide for 24 hr reduced cell proliferation and caused an increase in multinucleated cells because of inhibition of cytokinesis. Exposure of Day 5 embryos to a heat shock of 41 degrees C for 15 hr increased neutral sphingomyelinase activity but did not change acid sphingomyelinase activity. In conclusion, ceramide can regulate embryo development and apoptosis in a time and stage-of-development dependent manner and ceramide generation can be activated by cellular insult. Thus, the ceramide signaling pathway is present in the preimplantation embryo.

Therapeutic efficacy of Ac-DMQD-CHO, a caspase 3 inhibitor, for rat spinal cord injury

We investigated the therapeutic efficacy of Ac-DMQD-CHO, a caspase-3 inhibitor, and functional recovery in spinal cord injury in a rat model. Thirty rats were randomized into three groups of 10 each. In groups 2 and 3, spinal cord trauma was produced in the thoracic region. Group 3 rats were treated with Ac-DMQD-CHO. Treatment responses were evaluated based on histopathological and TUNEL staining findings at 24 h and 5 days post-injury. Neurologic performance was assessed during and following treatment. Twenty-four hours after injury, light microscopy examination revealed diffuse hemorrhagic necrosis, edema, vascular thrombi, and polymorphonuclear leukocyte infiltration in group 2 and 3 rats, but cavitation and demyelinization were less prominent in group 3. At this time point, treatment of the rats with Ac-DMQD-CHO significantly reduced the number of apoptotic cells. Traumatic injury to the spinal cord causes apoptosis and administration of Ac-DMQD-CHO decreases apoptosis and improves functional outcome.

Heat shock induced apoptosis in normal and tumor human umbilical vein cells (HUVECs)

Human endothelial cell injury may play an important role tumor damage hyperthermia in vivo. In this study, human umbilical vein cells were heat shocked in vitro at different temperatures (41-55 degrees C). Cells were observed 0, 12, 24, 36, 48, 60 and 72 hours after heat shock. By incrementally increasing the heat load from 41-55 degrees C, we observed a gradually increase in apoptosis with a significant change from apoptotic to necrotic death at temperature beyond 45 degrees C. Further, an in vitro human breast tumor endothelial cell model was established to compare the heat shock response between normal and tumor endothelial cells.

Anti-apoptotic effect of retinoic acid on retinal progenitor cells mediated by a protein kinase A-dependent mechanism

Retinal progenitor cells (RPCs) are neural stem cells able to differentiate into any normal adult retinal cell type, except for pigment epithelial cells. Retinoic acid (RA) is a powerful growth/differentiation factor that generally causes growth inhibition, differentiation and/or apoptosis. In this study, we demonstrate that RA not only affects mouse RPC differentiation but also improves cell survival by reducing spontaneous apoptotic rate without affecting RPC proliferation. The enhanced cell survival was accompanied by a significant upregulation of the expression of protein kinase A (PKA) and several protein kinase C (PKC) isoforms. Treatment of cells grown in RA-free media with 8-bromoadenosine3',5'-cyclic monophosphate, a known activator of PKA, resulted in an anti-apoptotic effect similar to that caused by RA; whereas the PKA inhibitor N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride led to a significant ( approximately 32%) increase in apoptosis. In contrast, treatment of RPCs with any of two PKC selective inhibitors, 2,2',3,3',4,4'-hexahydroxy-1,1'-biphenyl-6,6'-dimethanol dimethyl ether and bisindolylmaleimide XI, led to diminished apoptosis; while a PKC activator, phorbol 12-myristate 13-acetate, increased apoptosis. These and other data suggest that the effect of RA on RPC survival is mostly due to the increased anti-apoptotic activity elicited by PKA, which might in turn be antagonized by PKC. Such a mechanism is a new example of tight regulation of important biological processes triggered by RA. Although the detailed mechanisms remain to be elucidated, we provide evidence that the pro-survival effect of RA on RPCs is not mediated by changed expression of p53 or bcl-2, and appears to be independent of beta-amyloid, Fas ligand, TNF-alpha, ganglioside GM1 and ceramide C16-induced apoptotic pathways.

Evaluation of cancer-preventive activity and structure-activity relationships of 3-demethylubiquinone Q2, isolated from the ascidian Aplidium glabrum, and its synthetic analogs

PURPOSE

3-Demethylubiquinone Q2 was isolated from the ascidian Aplidium glabrum. The cancer-preventive properties and the structure-activity relationship for 3-demethylubiquinone Q2 and 12 of its synthetic analogs are reported.

METHODS

Compounds, having one or several di- or triprenyl substitutions and quinone moieties with methoxyls in different positions, were synthesized. The cancer-preventive properties of compounds and were tested in JB6 Cl41 mouse skin cells, using a variety of assessments, including the methanethiosulfonate (MTS) assay, flow cytometry, and soft agar assay. Statistical nonparametric methods were used to confirm statistical significance.

RESULTS

All quinones tested were shown to inhibit JB6 Cl41 cell transformation, to induce apoptosis, AP-1, and NF-kappaB activity, and to inhibit p53 activity. The most promising effects were indicated for compounds containing two isoprene units in a side chain and a methoxyl group at the para-position to a polyprenyl substitution.

CONCLUSIONS

Quinones and demonstrated cancer-preventive activity in JB6 Cl41 cells, which may be attributed to the induction of p53-independent apoptosis. These activities depended on the length of side chains and on the positions of the methoxyl groups in the quinone part of the molecule.

Neutral sphingomyelinases and nSMase2: Bridging the gaps

There is strong evidence indicating a role for ceramide as a second messenger in processes such as apoptosis, cell growth and differentiation, and cellular responses to stress. Ceramide formation from the hydrolysis of sphingomyelin is considered to be a major pathway of stress-induced ceramide production with magnesium-dependent neutral sphingomyelinase (N-SMase) identified as a prime candidate in this pathway. The recent cloning of a mammalian N-SMase-nSMase2- and generation of nSMase2 knockout/mutant mice have now provided vital tools with which to further study the regulation and roles of this enzyme in both a physiological and pathological context. In the present review, we summarize current knowledge on N-SMase relating this to what is known about nSMase2. We also discuss the future areas of nSMase2 research important for molecular understanding of this enzyme and its physiological roles.

Transcriptional regulation of caspases in experimental pneumococcal meningitis

Apoptosis and necrosis in brain account for neurological sequelae in survivors of bacterial meningitis. In meningitis, several mechanisms may trigger death pathways leading to activation of transcription factors regulating caspases mRNA synthesis. Therefore, we used a multiprobe RNA protection assay (RPA) to examine the expression of 9 caspase-mRNA in the course of experimental Streptococcus pneumoniae meningitis in mouse brain. Caspase-6, -7 and -11 mRNA were elevated 6 hours after infection. 12 hours after infection caspases-1, -2, -8 and -12 mRNA rose. Caspase-14 mRNA was elevated 18 h and caspase-3 mRNA 24 h after infection. In situ hybridization detected caspases-3, -8, -11 and -12 mRNA in neurons of the hippocampal formation and neocortex. Development of sepsis was paralleled by increased transcription of caspases mRNA in the spleen. In TNFalpha-deficient mice all caspases examined were less upregulated, in TNF-receptor 1/2 knockout mice caspases-1, -2, -7, -11 and -14 mRNA were increased compared to infected control animals. In caspase-1 deficient mice, caspases-11, and -12 mRNA levels did not rise in meningitis indicating the necessity of caspase-1 activating these caspases. Hippocampal formations of newborn mice incubated with heat-inactivated S. pneumoniae R6 showed upregulation of caspase-1, -3, -11 and -12 mRNA. These observations suggest a tightly regulated caspases network at the transcriptional level in addition to the known cascade at the protein level.

Role of c-Fos protein on glutamate toxicity in primary neural hippocampal cells

The hippocampus is extremely sensitive to microenvironmental signals and toxic events, including massive glutamate release. Despite the extensive literature related to the cascade of molecular events triggered in postsynaptic neurons, the distinction between proapoptotic and survival pathways is still being discussed. In this study, we have investigated the role of c-Fos in glutamate-induced toxicity in primary cultures of hippocampal neurons by using antisense oligonucleotide (ASO) technology. Exposure of cells (5 days in vitro; DIV) to glutamate 0.5 mM for 24 hr caused massive nuclear alteration. An increase in the number of caspase-3-positive cells was also observed 24 hr after glutamate treatment. The expression of c-fos and c-jun immediate-early genes was increased 30 min after glutamate exposure. The study of c-Fos and c-Jun protein expression revealed an increase in the number of cells positive for both antibodies. To investigate whether the expression of c-Fos protein after glutamate treatment was related to cell death activation or cell survival pathways, cells were exposed to 5 microM of c-fos ASO at 4 DIV, 24 hr before glutamate treatment. The presence of the ASO in the medium significantly decreased the number of altered nuclei, and this was associated with a significant reduction in the number of c-Fos-positive cells after glutamate treatment. Exposure of cells to the c-fos ASO under the conditions described above decreased caspase-3 immunostaining induced by glutamate. These results suggest that the synthesis of c-Fos protein after glutamate exposure favors cell death pathway activation in which caspase-3 is also involved.

Analysis of gene expression in apoptosis of human lymphoma U937 cells induced by heat shock and the effects of α-phenyl N-tert-butylnitrone (PBN) and its derivatives

Hyperthermia, a modality of cancer therapy, has been known as a stress to induce apoptosis. However, the molecular mechanism of heat shock-induced apoptosis, especially on roles of intracellular oxidative stress, is not fully understood. First, when human lymphoma U937 cells were treated with heat shock (44 degrees C, 30 min), the fraction of apoptosis, revealed by phosphatidylserine externalization, increased gradually and peaked at 6 hr after the treatment. In contrast, intracellular superoxide formation increased early during the heat shock treatment and peaked at 30 min after the treatment. When the cells were treated with heat shock in the presence of alpha -phenyl-N-tert-butylnitrone (PBN) and its derivatives, which are potent antioxidants, the DNA fragmentation was inhibited in an order according to the agents' hydrophobicity. PBN showing the highest inhibitory effects suppressed not only intracellular superoxide formation but also various apoptosis indicators. cDNA microarray was employed to analyze gene expression associated with heat shock-induced apoptosis, and the time-course microarray analysis revealed 5 groups showing changes in their pattern of gene expression. Among these genes, c-jun mRNA expression showed more than 40 fold increase 2 hr after heat treatment. The expression level of c-jun mRNA verified by quantitative real-time PCR was about 20 fold increase, and c-jun expression was similarly suppressed by PBN and its derivatives. These results suggest that the change of c-jun expression is an excellent molecular marker for apoptosis mediated by intracellular oxidative stress induced by heat shock.

Upregulation of ceramide and its regulating mechanism in a rat model of chronic cerebral ischemia

Ceramide is a key mediator of apoptosis, and is involved in the cellular stress response. We examined the alterations in the ceramide levels and their synthetic/degradative pathway in a rat model of chronic cerebral ischemia, in which ischemic white matter (WM) lesions occur in association with oligodendroglial cell apoptosis. Chronic cerebral ischemia was induced by clipping both common carotid arteries in male Wistar rats. After predetermined periods of 1, 3, 7 and 14 days, the animals were subjected to immunohistochemical and biochemical investigations for ceramide in the region containing the frontal cortex and corpus callosum (region 1), and the region containing the internal capsule and globus pallidus (region 2). After 14 days, the myelin was degraded in the corpus callosum, internal capsule and the optic tract in Klüver-Barrera staining. There was a significant increase in the ceramide level and the activity of its synthetic enzyme, acidic sphingomyelinase (SMase), whereas its degrading enzyme, glucosylceramide synthase (GCS), was downregulated in both regions 1 and 2 as compared to the sham-operated rats. Simultaneously, ceramide immunoreactive glia increased in number in the corpus callosum and the internal capsule after 3, 7 and 14 days. Double labeling for ceramide with glial fibrillary acidic protein but not with leukocyte common antigen indicated the astroglial nature of these glia. These findings indicate that chronic cerebral ischemia induces an increased ceramide level in astroglia as a result of downregulation of GCS and an upregulation of ASMase activity.

Acid and neutral sphingomyelinases: roles and mechanisms of regulation

Ceramide, an emerging bioactive lipid and second messenger, is mainly generated by hydrolysis of sphingomyelin through the action of sphingomyelinases. At least two sphingomyelinases, neutral and acid sphingomyelinases, are activated in response to many extracellular stimuli. Despite extensive studies, the precise cellular function of each of these sphingomyelinases in sphingomyelin turnover and in the regulation of ceramide-mediated responses is not well understood. Therefore, it is essential to elucidate the factors and mechanisms that control the activation of acid and neutral sphingomyelinases to understand their the roles in cell regulation. This review will focus on the molecular mechanisms that regulate these enzymes in vivo and in vitro, especially the roles of oxidants (glutathione, peroxide, nitric oxide), proteins (saposin, caveolin 1, caspases), and lipids (diacylglycerol, arachidonic acid, and ceramide).

Ceramide reduction and transcriptional up-regulation of glucosylceramide synthase through doxorubicin-activated Sp1 in drug-resistant HL-60/ADR cells

Treatment with doxorubicin (DOX) induced apoptosis with an increase of ceramide content in drug-sensitive HL-60 cells, but not in drug-resistant HL-60/ADR cells. In HL-60/ADR cells (but not in HL-60 cells), the levels of mRNA, protein, and activity in glucosylceramide synthase (GCS), which converts ceramide to glucosylceramide, were up-regulated in response to DOX. Thus, abrogation of apoptosis in HL-60/ADR cells might be involved in ceramide reduction through DOX-induced up-regulation of GCS function. Because we reported that a GC-rich/Sp1 promoter binding region was of importance in the regulation of GCS expression, the role of Sp1 in DOX-induced up-regulation of GCS and apoptosis was investigated. DOX induced Sp1 activation in HL-60/ADR cells, as assessed by Sp1 gel shift and promoter-luciferase reporter assays, whereas transfection of double-stranded oligodeoxynucleotides (ODNs) containing a GC-rich/Sp1 region (Sp1 decoy ODNs) inhibited DOX-induced Sp1 activation. In addition, DOX-increased mRNA and enzyme activity in GCS were inhibited by Sp1 decoy, in conjunction with corresponding elevations of ceramide content. Moreover, DOX-induced apoptotic cell death was significantly increased in Sp1 decoy ODN-transfected HL-60/ADR cells over mock-transfected HL-60/ADR cells. Together, the results suggest that transcriptional up-regulation of GCS through DOX-induced activation of Sp1 is one potential mechanism to regulate ceramide increase and apoptosis in HL-60/ADR cells.

Involvement of c-Fos in fenretinide-induced apoptosis in human ovarian carcinoma cells

Fenretinide (HPR), a synthetic retinoid that exhibits lower toxicity than other retinoids, has shown preventive and therapeutic activity against ovarian tumors. Although the growth inhibitory effects of HPR have been ascribed to its ability to induce apoptosis, little is known about the molecular mechanisms involved. Since the proto-oncogene c-Fos has been implicated in apoptosis induction, we analyzed its role in mediating HPR response in a human ovarian carcinoma cell line (A2780) sensitive to HPR apoptotic effect. In these cells, HPR treatment caused induction of c-Fos expression, whereas such an effect was not observed in cells made resistant to HPR-induced apoptosis (A2780/HPR). Moreover, in a panel of other human ovarian carcinoma cell lines, c-Fos inducibility and HPR sensitivity were closely associated. Ceramide, which is involved in HPR-induced apoptosis, was also involved in c-Fos induction because its upregulation by HPR was reduced by fumonisin B(1), a ceramide synthase inhibitor. The causal relationship between c-Fos induction and apoptosis was established by the finding of an increased apoptotic rate in cells overexpressing c-Fos. Similarly to that observed for c-Fos expression, HPR treatment increased c-Jun expression in HPR-sensitive but not in HPR-resistant cells, suggesting the involvement of the transcription factor activating protein 1 (AP-1) in HPR-induced apoptosis. In gene reporter experiments, HPR stimulated AP-1 transcriptional activity and potentiated the AP-1 activity induced by 12-tetradecanoylphorbol 13-acetate. Furthermore, inhibition of AP-1 DNA binding, by transfecting A2780 cells with a dominant-negative Fos gene, caused decreased sensitivity to HPR apoptotic effects. Overall, the results indicate that c-Fos plays a role in mediating HPR-induced growth inhibition and apoptosis in ovarian cancer cells and suggest that c-Fos regulates these processes as a member of the AP-1 transcription factor.

Ceramide-induced apoptosis: role of catalase and hepatocyte growth factor

The aim of this study was to elucidate cellular mechanisms involved in ceramide-induced apoptosis and its attenuation by hepatocyte growth factor (HGF). Human retinal pigmented epithelial cells (RPE) incubated with C2 ceramide accumulated reactive oxygen species (ROS) in mitochondria and underwent apoptosis in a dose-dependent manner. Ceramide-treated cells showed increased caspase-3 activation and an increase in mitochondrial membrane permeability transition (MPT). Low doses of H2O2 (100 microM) alone induced negligible apoptosis; however, ceramide-induced apoptosis was significantly enhanced by co-incubation with H2O2 (100 microM). Furthermore, ceramide treatment significantly decreased catalase enzymatic activity and protein expression. HGF pretreatment (20 ng/ml) significantly inhibited ceramide-induced apoptosis and reduced the accumulation of ROS, the activation of caspase-3, and the increase in MPT and prevented the reduction in catalase activity and expression. Together, the data suggest that ceramide induces apoptosis in RPE cells by increasing ROS production, MPT, and caspase-3 activation. The ceramide effect is potentiated by H2O2 and associated with a reduction in catalase activity, suggesting that catalase plays a central role in regulating this apoptotic response. The ability of HGF to attenuate these effects demonstrates its effectiveness as an antioxidant growth factor.

Phyllanthus urinaria induces the Fas receptor/ligand expression and ceramide-mediated apoptosis in HL-60 cells

Phyllanthus urinaria (P. urinaria), a widely used herb medicine, was tested for the anticancer effect on human myeloid leukemia cells in this study. The water extract of P. urinaria induced the apoptosis of HL-60 cells as demonstrated by morphological change, DNA fragmentation and increased caspase-3 activity. However, normal human peripheral mononuclear cells remained viable under the same treatment. The P. urinaria-induced apoptosis of HL-60 cells was associated with the increased Bax gene expression and decreased Bcl-2 gene expression. In addition, the gene expressions of Fas receptor and Fas ligand, but not p53, were also induced in HL-60 cells dose- and time-dependently. The inhibitor of ceramide synthase, fumonisin B1, completely suppressed the apoptosis induced by P. urinaria and this inhibitory effect of fumonisin B1 could be eliminated by the addition of ceramide. It indicated that the activity of ceramide synthase is critical for the P. urinaria-induced apoptosis in HL-60 cells. The P. urinaria-induced apoptosis in HL-60 cells is mediated through a ceramide-related pathway.

Melatonin prevents apoptosis and enhances HSP27 mRNA expression induced by heat shock in HL-60 cells: possible involvement of the MT2 receptor

Previous studies have reported that melatonin protects cells and tissues against stressful stimuli. In the present study using HL-60 cells, we show that cells acquire increased resistance to apoptosis normally induced by heat shock when they are incubated with melatonin. This effect of melatonin is saturable at nanomolar concentrations and appears to be mediated by the MT2 subtype melatonin receptor. The high affinity melatonin receptor agonist, 2-iodomelatonin, reproduced the melatonin effect while it was fully blocked by the selective MT2 antagonist 4-phenyl-2-propionamidotetraline. The melatonin response to heat shock-induced apoptosis was pertussis toxin sensitive and, interestingly, the non-selective MT1/MT2 melatonin receptor ligand luzindole was found to display agonistic activity. Furthermore, we provide evidence that melatonin enhanced HSP27 mRNA expression as a result of heat shock - HSP27, is known to play an important role in the defense of cells against apoptosis induced by stressful agents. Together, these results demonstrate that melatonin, likely via receptor mechanisms, interferes with the apoptotic pathway activated by heat shock.

Bacterial ceramides and sphingophospholipids induce apoptosis of human leukaemic cells

The genus Sphingobacterium, whose members are Gram-negative non-fermentative rods, possesses ceramides and related sphingophospholipids (SPLs) with isoheptadecasphinganine and 2-hydroxy or non-hydroxy isopentadecanoic acid. This paper reports evidence that ceramides isolated from Sphingobacterium spiritivorum ATCC 33861 induce endonucleolytic DNA cleavage in human myeloid leukaemia HL-60 cells in vitro, which is the primary characteristic biochemical marker for apoptosis or programmed cell death. Ceramides and SPLs also induced DNA fragmentation and caspase-3 activation, followed by changes in morphology, such as alterations in the size of nuclei and cells, and cell cycle shortening. Apoptotic activity correlated with the ceramide structure. Ceramide with a 2-hydroxy fatty acid showed stronger apoptotic activity than ceramide with a non-hydroxy fatty acid. Furthermore, the major five SPLs (ceramide phosphorylethanolamine-1 and -2, ceramide phosphorylinositol-1 and -2, and ceramide phosphorylmannose-1) showed apoptosis-inducing activity in HL-60 cells, indicating that the ceramide moiety of the SPLs plays a crucial role as the intracellular second messenger but that their hydrophilicity is less important in this regard. The hydrophilic part of SPLs may play a role in other cellular response systems. The involvement of Fas antigen was implicated in the apoptotic event since Fas antigen expression was observed after 3 or 4 h stimulation of HL-60 cells with bacterial ceramides. However, a time-course study for caspase-3 activation indicated maximal activity at 1 h after stimulation with bacterial ceramides, suggesting that two (or possibly more) mechanisms of signal transduction, Fas-dependent and Fas-independent, may be involved. Fas antigen expression and caspase-3 activation by five kinds of SPLs were observed after 3 or 4 h. These results indicate that there is a difference in the response of HL-60 cells to bacterial ceramides and SPLs.

Protein kinase C epsilon dependence of the recovery from down-regulation of S1P1 G protein-coupled receptors of T lymphocytes

Sphingosine 1-phosphate (S1P) from mononuclear phagocytes and platelets signals T cells predominantly through S1P1 G protein-coupled receptors (Rs) to enhance survival, stimulate and suppress migration, and inhibit other immunologically relevant responses. Cellular S1P1 Rs and their signaling functions are rapidly down-regulated by S1P, through a protein kinase C (PKC)-independent mechanism, but characteristics of cell-surface re-expression of down-regulated S1P1 Rs have not been elucidated. T cell chemotactic responses (CT) to 10 and 100 nm S1P and inhibition of T cell chemotaxis to chemokines (CI) by 1 and 3 microm S1P were suppressed after 1 h of preincubation with 100 nm S1P, but recovered fully after 12-24 h of exposure to S1P. Late recovery of down-regulated CT and CI, but not early down-regulation, was suppressed by PKC and PKCepsilon-selective inhibitors and was absent in T cells from PKCepsilon-null mice. The same PKCepsilon inhibitors blocked S1P-evoked increases in T cell nuclear levels of c-Fos and phosphorylated c-Jun and JunD after 24 h, but not 1 h. A mixture of c-Fos plus c-Jun antisense oligonucleotides prevented late recovery of down-regulated CT and CI, without affecting S1P induction of down-regulation. Similarly, S1P-elicited threonine phosphorylation of S1P1 Rs was suppressed by a selective inhibitor of PKCepsilon after 24 h, but not 1 h. Biochemical requisites for recovery of down-regulated S1P1 Rs thus differ from those for S1P induction of down-regulation.

Androgen and the blocking of radiation-induced sensitization to Fas-mediated apoptosis through c-jun induction in prostate cancer cells

PURPOSE

To clarify the key mechanism by which androgen makes prostate cancer cells highly resistant to Fas-mediated apoptosis.

MATERIALS AND METHODS

The role of c-jun induction by 10 nM dihydrotestosterone (DHT) in 5 Gy radiation-induced up-regulation of Fas and sensitization to the apoptosis was studied by using the human prostate cancer cell line LNCaP.

RESULTS

On exposure to 5 Gy radiation, LNCaP cells demonstrated high sensitization to Fas-mediated apoptosis through increased Fas expression, stabilized p53 expression and binding to p53 response elements within the promoter and first intronic region of the Fas gene. Following treatment with DHT, in vivo binding of p53 to its response elements was strongly inhibited. In addition, DHT significantly up-regulated c-jun expression through extracellular stress-regulated kinase (ERK) activation, and transfection of an antisense oligonucleotide for c-jun or ERK inhibition by PD98059 cancelled DHT-mediated suppression of radiation-induced transactivation of Fas gene and sensitization to Fas-mediated apoptosis.

CONCLUSIONS

Radiation-induced Fas sensitization in prostate cancer cell was mediated through p53-dependent transactivation of the Fas gene, which can be blocked by androgen stimulation mainly through induction of c-jun.

Ceramide induces cell cycle arrest and upregulates p27kip in nasopharyngeal carcinoma cells

Ceramide mediates differentiation, growth arrest, apoptosis, proliferation, cytokine biosynthesis and secretion, and a variety of other cellular functions. However, little is known regarding ceramide signaling linked to the cell cycle. In the present study, the effect of ceramide on cell cycle in nasopharyngeal carcinoma cell line CNE2 was investigated. The results showed that ceramide inhibited cell proliferation and induced cell cycle arrest in G1 phase in CNE2 cells. Exposure of CNE2 cells to ceramide resulted in a dose-dependent up-regulation of the cyclin-dependent kinase inhibitor p27 and a decrease of phospho-Akt without reduced expression of total AKT protein. The activation of phosphatidylinositol-3-kinase (PI3K) and the protein expression of PTEN were unaffected following ceramide treatment. We concluded that ceramide induced cell cycle arrest in G1 phase in CNE2 cells and p27 up-regulation was involved in this process. In addition, up-regulation of p27 resulting from ceramide treatment may be due to the interruption of Akt, but decrease of phospho-Akt is independent of PI3K function or PTEN protein expression.

Ceramide increases oxidative damage due to inhibition of catalase by caspase-3-dependent proteolysis in HL-60 cell apoptosis

We investigated through which mechanisms ceramide increased oxidative damage to induce leukemia HL-60 cell apoptosis. When 5 microm N-acetylsphingosine (C(2)-ceramide) or 20 microm H(2)O(2) alone induced little increase of reactive oxygen species (ROS) generation as judged by the 2'-7'-dichlorofluorescin diacetate method, 20 microm H(2)O(2) enhanced oxidative damage as judged by ROS accumulation, and thiobarbituric acid-reactive substance production after pretreatment with 5 microm C(2)-ceramide at least for 12 h. The treatment with a catalase inhibitor, 3-amino-1h-1,2,4-triazole, increased oxidative damage and apoptosis induced by H(2)O(2), and in contrast, purified catalase inhibited the enhancement of oxidative damage by H(2)O(2) in ceramide-pretreated cells, suggesting that the oxidative effect of ceramide is involved in catalase regulation. Indeed, C(2)-ceramide inhibited the activity of immunoprecipitated catalase and decreased the levels of catalase protein in a time-dependent manner. Moreover, acetyl-Asp-Met-Gln-Asp-aldehyde, which dominantly inhibited caspase-3 and blocked the increase of oxidative damage and apoptosis due to C(2)-ceramide-induced catalase depletion at protein and activity levels. In vitro, active and purified caspase-3, but not caspase-6, -8, and -9, inhibited catalase activity and induced the proteolysis of catalase protein whereas these in vitro effects of caspase-3 were blocked by acetyl-Asp-Met-Gln-Asp-aldehyde. Taken together, it is suggested that H(2)O(2) enhances apoptosis in ceramide-pretreated cells, because ceramide increases oxidative damage by inhibition of ROS scavenging ability through caspase-3-dependent proteolysis of catalase.

Requirement of c-jun for testosterone-induced sensitization to N-(4-hydroxyphenyl)retinamide-induced apoptosis

Androgen stimulation strongly affects the sensitivity to anticancer drug-induced apoptosis in prostate cancer cells. We investigated the influence of androgen stimulation with testosterone on N-(4-hydroxyphenyl)retinamide (4-HPR)-induced apoptosis in the androgen-sensitive prostate cancer cell line LNCaP. Overexpression of a dominant negative form of mitogen-activated protein kinase kinase 7, a specific kinase of c-jun NH(2)-terminal kinase (JNK), significantly inhibited 4-HPR-induced JNK activation and apoptosis and canceled the hormone-dependent sensitization. Testosterone activated extracellular signal-regulated kinase (ERK), activating protein-1, subsequently increased the expression of c-jun. In addition, testosterone significantly enhanced in vivo phosphorylation of c-jun by 4-HPR as well as JNK activation. Transfection with an antisense oligonucleotide of c-jun blocked 4-HPR-induced apoptosis and the testosterone-induced sensitization, suggesting a major contribution of the JNK/c-jun mediated pathway in androgen-dependent sensitization. Interestingly, inhibition of testosterone-induced activation by PD98059 also canceled an upregulation of c-jun and increased apoptosis. These results suggested that modulation of JNK activation and expression of c-jun through ERK might have been essentially involved in androgen-mediated sensitization to 4-HPR-induced apoptosis in prostate cancer cells.

Inducing cancer cell death by targeting transcription factors

We review the biological significance of transcription factors such as p53, Myc, E2F family and AP-1 (Jun/Fos) in anticancer drug-induced apoptosis. It is likely that the functional role of these transcription factors is complex in response to DNA damage depending on cancer cell type. Regulation of apoptosis following DNA damage is mediated by cell cycle arrest for DNA repair and subsequent signal transduction pathways leading to apoptosis, which is associated with mitochondrial dysfunction. Activation of transcription factors following anticancer drugs is located upstream of signal transduction pathways, thereby the downstream pathway is promoted, which is connected to activation or suppression of apoptosis-related proteins. Switching on apoptotic signals by anticancer drugs is amplified in mitochondria by releasing cytochrome from the ion channel to activate the caspase cascade, which is regulated by Bcl-2 families in the central gate for drug-induced apoptosis. Activation of transcription factors targeting downstream genes, some of which are apoptosis-related genes, can play a critical role in promoting apoptosis following treatment with anticancer drugs. The strategy of identification of downstream target proteins or transcription factors involved in apoptosis will be necessary for the development of an effective transcription factor-targeted chemotherapy for cancer.

Sphingomyelin hydrolysis during apoptosis

Sphingolipid breakdown products are now being recognized as important players in apoptosis. Ceramide, which is considered to serve as second messenger, is mainly generated by hydrolysis of the membrane sphingophospholipid sphingomyelin (SM) through the action of a sphingomyelinase (SMase). However, little is known about the localization and regulation of this phenomenon. Here, we summarize the current knowledge on the function of SM hydrolysis in apoptosis signaling. In particular, the present review focuses on the role of neutral sphingomyelinase (N-SMase) in the generation of the proapoptotic ceramide. This enzyme is regulated by several mechanisms, including the tumor necrosis factor (TNF) receptor-associated protein FAN (for factor associated with N-SMase activation) and oxidative stress. These observations place SMase activation and SM hydrolysis as early events in the apoptosis signaling cascade.

Acute activation of de novo sphingolipid biosynthesis upon heat shock causes an accumulation of ceramide and subsequent dephosphorylation of SR proteins

Recent studies are beginning to implicate sphingolipids in the heat stress response. In the yeast Saccharomyces cerevisiae, heat stress has been shown to activate de novo biosynthesis of sphingolipids, whereas in mammalian cells the sphingolipid ceramide has been implicated in the heat shock responses. In the current study, we found an increase in the ceramide mass of Molt-4 cells in response to heat shock, corroborating findings in HL-60 cells. Increased ceramide was determined to be from de novo biosynthesis by two major lines of evidence. First, the accumulation of ceramide was dependent upon the activities of both ceramide synthase and serine palmitoyltransferase. Second, pulse labeling studies demonstrated increased production of ceramide through the de novo biosynthetic pathway. Significantly, the de novo sphingolipid biosynthetic pathway was acutely induced upon heat shock, which resulted in a 2-fold increased flux in newly made ceramides within 1-2 min of exposure to 42.5 degrees C. Functionally, heat shock induced the dephosphorylation of the SR proteins, and this effect was demonstrated to be dependent upon the accumulation of de novo-produced ceramides. Thus, these studies disclose an evolutionary conserved activation of the de novo pathway in response to heat shock. Moreover, SR dephosphorylation is emerging as a specific downstream target of accumulation of newly made ceramides in mammalian cells.

Increase of ceramide in adriamycin-induced HL-60 cell apoptosis: detection by a novel anti-ceramide antibody

We recently raised an IgM class of monoclonal antibody (Ab) for ceramide (NHCER-2), and examined its specificity and sensitivity. Enzyme-linked immunosorbent assay (ELISA) and thin-layer chromatography (TLC) showed that NHCER-2 recognized ceramides but not other sphingolipids such as sphingosine, sphinganine, sphingomyelin, sphingosine-1-phosphate, ceramide-1-phosphate, glucosylceramide and cerebroside. In addition, N-hexanoyl, N-octanoyl and N-palmitoylsphingosine were detected by NHCER-2, but N-acetylsphingosine and dihydroceramide were not. Densities of ceramide detected by NHCER-2 were proportional to the amounts of ceramide standard up to 250 ng. When various concentrations of adriamycin (ADR) was added to induce apoptosis, the amounts of ceramide detected by NHCER-2 time- and dose-dependently increased in apoptosis-sensitive HL-60 cells as well as by DGK assay, but not in apoptosis-resistant HL-60/ADR cells. After cell fractionation, ceramide levels judged not only by diacylglycerol kinase (DGK) assay but also by NHCER-2 were shown to increase in the microsomal and the nuclear fraction in apoptosis-sensitive cells, but not in apoptosis-resistant cells. Moreover, absolute amounts of ceramide determined by NHCER-2 were well correlated with those by DGK assay. These results suggest that increase of ceramide in the nuclear fraction as well as in the microsomal fraction may play a role in ADR-induced apoptosis and that a novel anti-ceramide Ab NHCER-2 could be beneficial to investigate changes of ceramide content in the cells.

The effects of vitamin E succinate on the expression of c-jun gene and protein in human gastric cancer SGC-7901 cells

AIM

To investigate the effects of vitamin E succinate (VES) on the expression of c-jun gene and protein in human gastric cancer SGC-7901 cells.

METHODS

After SGC-7901 cells were treated with VES at different doses (5,10,20 mg x L(-1)) at different time, reverse transcription-PCR technique was used to detect the level of c-jun mRNA; Western Blot was applied to measure the expression of c-jun protein.

RESULTS

After the cells were treated with VES at 20 mg x L(-1) for 3 h, the expression rapidly reached its maximum that was 3.5 times of UT control (P<0.01). The level of c-jun mRNA was also increased following treatment of VES for 6 h. However,the expression after treatment of VES at 5 mg x L(-1) for 24 h was 1.6 times compared with UT control (P<0.01). Western blot analysis showed that the level of c-jun protein was obviously elevated in VES-treated SGC-7901 cells at 20 mg x L(-1) for 3 h. The expression of c-jun protein was gradually increased after treatment of VES at 20 mg x L(-1) for 3, 6, 12 and 24 h, respectively, with an evident time-effect relationship.

CONCLUSION

The levels of c-jun mRNA and protein in VES-treated SGC-7901 cells were increased in a dose- and time-dependent manner; the expression of c-jun was prolonged by VES, indicating that c-jun is involved in VES-induced apoptosis in SGC-7901 cells.

Relationship between the activation of heat shock factor and the suppression of nuclear factor-kappaB activity in rat hepatocyte cultures treated with cyclosporine A

We investigated on primary cultures of rat hepatocytes the effect of cyclosporine A (CsA) on the activation of nuclear factor-kappaB (NF-kappaB), activator protein 1 (AP-1), and heat shock factor 1 (HSF1), three transcription factors involved in cellular response pathways. Hepatocytes were subjected to a time-course (1, 3, 6, and 22 hr) incubation and CsA treatment in the range 1-50 microM. NF-kappaB, AP-1, and HSF1 binding activities were established through electrophoretic mobility shift assay. Levels of HSP70 mRNA and protein were measured by Northern and Western blot analysis respectively. In cells incubated for 1 and 3 hr, electrophoretic mobility shift assay experiments showed a dose-dependent increase of the NF-kappaB binding activity; while following 22hr of incubation, a suppression of the positive effect of CsA at shorter times was detected. At all periods of incubation assayed, CsA induced the activation of AP-1 which was detected by DNA-binding activity of this transcription factor. A dose-dependent activation of HSF1 was observed at 22 hr of incubation. We conclude that in rat hepatocyte cultures, CsA induces the transcriptional activation of NF-kappaB, AP-1, and HSF1. However, the time point at which activation of each transcription factor occurs is different. Thus, at 22 hr of incubation, the CsA-induced activation of HSF1 is accompanied by the reduction of the positive effect of CsA on NF-kappaB activation at earlier time points.