Caspase Activation Is Required for Nitric Oxide–Mediated, CD95(APO-1/Fas)–Dependent and Independent Apoptosis in Human Neoplastic Lymphoid Cells

Antioxidant and Signal-Modulating Effects of Brown Seaweed-Derived Compounds against Oxidative Stress-Associated Pathology

The biological and therapeutic properties of seaweeds have already been well known. Several studies showed that among the various natural marine sources of antioxidants, seaweeds have become a potential source of antioxidants because of their bioactive compounds. Most of the metabolic diseases are caused by oxidative stress. It is very well known that antioxidants have a pivotal role in the treatment of those diseases. Recent researches have revealed the potential activity of seaweeds as complementary medicine, which have therapeutic properties for health and disease management. Among the seaweeds, brown seaweeds (Phaeophyta) and their derived bioactive substances showed excellent antioxidant properties than other seaweeds. This review focuses on brown seaweeds and their derived major bioactive compounds such as sulfated polysaccharide, polyphenol, carotenoid, and sterol antioxidant effects and molecular mechanisms in the case of the oxidative stress-originated disease. Antioxidants have a potential role in the modification of stress-induced signaling pathways along with the activation of the oxidative defensive pathways. This review would help to provide the basis for further studies to researchers on the potential antioxidant role in the field of medical health care and future drug development.

Nitric Oxide in Hematological Cancers: Partner or Rival?

Significance: Hematological malignancies represent the fourth most diagnosed cancer. Relapse and acquired resistance to anticancer therapy constitute two actual issues that need to be overcome. Nitric oxide (NO) plays a pivotal role in regulating cancer progression. At present, many studies are attempting to uncover the potentials of modulating NO levels to improve the efficacy of currently available treatments against lymphoma, leukemia, and myeloma. Recent Advances: It is becoming progressively clear that NO modulation may help hematological cancer management, either by targeting directly tumor cells or by driving the immune system to eliminate cancer cells. Critical Issues: NO is a dual molecule that can have a tumor-protecting or stimulating effect, depending on its local concentration. Moreover, NO is able to target a wide range of molecules involved in both cancer genesis and evolution. In this review, an overview of the recent findings regarding the pivotal role played by NO and nitric oxide synthase in cancer progression and anticancer therapy is presented, with particular focus on hematological malignancies. Future Directions: It is critical to establish the cancer-specific function of NO and critically drive its modulation to improve cancer management toward a personalized approach. This has a special importance in hematological tumors, where the urgency of finding eradicative therapies is constant. Antioxid. Redox Signal. 34, 383-401.

Breaking Therapy Resistance: An Update on Oncolytic Newcastle Disease Virus for Improvements of Cancer Therapy

Resistance to therapy is a major obstacle to cancer treatment. It may exist from the beginning, or it may develop during therapy. The review focusses on oncolytic Newcastle disease virus (NDV) as a biological agent with potential to break therapy resistance. This avian virus combines, upon inoculation into non-permissive hosts such as human, 12 described anti-neoplastic effects with 11 described immune stimulatory properties. Fifty years of clinical application of NDV give witness to the high safety profile of this biological agent. In 2015, an important milestone was achieved, namely the successful production of NDV according to Good Manufacturing Practice (GMP). Based on this, IOZK in Cologne, Germany, obtained a GMP certificate for the production of a dendritic cell vaccine loaded with tumor antigens from a lysate of patient-derived tumor cells together with immunological danger signals from NDV for intracutaneous application. This update includes single case reports and retrospective analyses from patients treated at IOZK. The review also presents future perspectives, including the concept of in situ vaccination and the combination of NDV or other oncolytic viruses with checkpoint inhibitors.

IFNγ and TNFα synergistically induce apoptosis of mesenchymal stem/stromal cells via the induction of nitric oxide

BACKGROUND

Mesenchymal stem/stromal cells (MSCs) have been widely used to treat various inflammatory diseases. The immunomodulatory capabilities of MSCs are usually licensed by inflammatory cytokines and may vary depending on the levels and the types of inflammatory cytokines. However, how the inflammatory microenvironment affects the fate of MSCs remains elusive. Here we characterized the molecular mechanism underlying the apoptosis of mouse MSCs triggered by the synergistic action of IFNγ and TNFα.

METHODS

We isolated and expanded MSCs by flushing the femoral and tibial bone marrow of wild-type, iNOS^-/-, and Fas^-/- mice. BM-MSCs were treated with IFNγ and TNFα in vitro, and cell viability was evaluated by a CCK-8 kit. Apoptosis was assessed by Annexin V/propidium iodide-stained flow cytometry. Expression of genes related to apoptosis and endoplasmic reticulum (ER) stress was measured by reverse transcription-polymerase chain reaction (RT-PCR). Apoptosis and autophagy-related proteins were examined by Western blot analysis.

RESULTS

IFNγ and TNFα synergistically trigger apoptosis of mouse BM-MSCs. The two cytokines were shown to stimulate the expression of inducible nitric oxide synthase (iNOS) and consequently the generation of nitric oxide (NO), which is required for the apoptosis of mouse BM-MSCs. The two cytokines similarly induced apoptosis in Fas^-/- BM-MSCs. iNOS and NO were shown to upregulate Fas in mouse MSCs and sensitize them to Fas agonist-induced apoptosis. Moreover, NO stimulated by IFNγ/TNFα impairs autophagy, which aggravates ER stress and promotes apoptosis.

CONCLUSIONS

IFNγ/TNFα-induced apoptosis in mouse MSCs is mediated by NO. Our findings shed new light on cytokine-induced apoptosis of MSCs and have implications in MSC-based therapy of inflammatory diseases.

The Inflammasome: Regulation of Nitric Oxide and Antimicrobial Host Defence

Nitric oxide (NO) is a gaseous signalling molecule that plays diverse physiological functions including antimicrobial host defence. During microbial infection, NO is synthesized by inducible NO synthase (iNOS), which is expressed by host immune cells through the recognition of microbial pattern molecules. Therefore, sensing pathogens or their pattern molecules by pattern recognition receptors (PRRs), which are located at the cell surface, endosomal and phagosomal compartment, or in the cytosol, is key in inducing iNOS and eliciting antimicrobial host defence. A group of cytosolic PRRs is involved in inducing NO and other antimicrobial molecules by forming a molecular complex called the inflammasome. Assembled inflammasomes activate inflammatory caspases, such as caspase-1 and caspase-11, which in turn process proinflammatory cytokines IL-1β and IL-18 into their mature forms and induce pyroptotic cell death. IL-1β and IL-18 play a central role in immunity against microbial infection through activation and recruitment of immune cells, induction of inflammatory molecules, and regulation of antimicrobial mediators including NO. Interestingly, NO can also regulate inflammasome activity in an autocrine and paracrine manner. Here, we discuss molecular mechanisms of inflammasome formation and the inflammasome-mediated regulation of host defence responses during microbial infections.

Cellular and plasma nitrite levels in myeloid leukemia: a pathogenetic decrease

Nitric oxide (NO) has a contributory role in hemopoietic cell growth and differentiation. The effects of NO on leukemic cell growth have been predominantly studied inin vitrosettings. This study was done to assess the alterations in nitrite level in myeloid leukemias. Thirty-six newly diagnosed cases of myeloid leukemia (16 AML and 20 CML) were enrolled in the study. Neutrophil precursors from the marrow aspirate and peripheral blood were separated into cell bands using the Percoll density gradient method of Borregard and Cowland. The blood plasma and marrow fluid was also collected. Nitrite (stable non-volatile end product of NO) was estimated in the cell bands, blood plasma and marrow fluid using Griess reagent. The mean nitrite level in all cell bands from peripheral blood, bone marrow, blood plasma, and marrow fluid of cases was significantly lower as compared to corresponding value in the controls. No significant difference between AML and CML was seen. On follow-up, analysis of 13 CML patients higher nitrite levels were seen (p>0.05). The significant decrease in nitrite levels in myeloid leukemia suggests a decrease in nitric oxide synthase (NOS) activity. Further work may unfold molecular targets for therapeutic role of NO modulators.

TNF-α and IFN-γ are potential inducers of Fas-mediated keratinocyte apoptosis through activation of inducible nitric oxide synthase in toxic epidermal necrolysis

Toxic epidermal necrolysis (TEN) is a severe immune-mediated adverse cutaneous drug eruption characterized by rapid and extensive epithelial cell death in the epidermis and mucosae. The molecular events leading to this often fatal condition are only partially understood, but evidence suggests a dual mechanism implicating a "drug"-specific immune response on one side and the onset of target cell death by proapoptotic molecules including FasL on the other side. Herein, we describe a potential molecular bridge between these two events that involves inducible nitric oxide synthase (iNOS), which is highly upregulated in the skin of TEN patients. We show that activated T cells secrete high amounts of tumor necrosis factor-α (TNF-α) and IFN-γ, and that both cytokines lead to increased expression and activity of keratinocyte iNOS. A similar observation has been made with drug-specific T lymphocytes from a TEN patient exposed to the culprit drug. The resulting increase in nitric oxide significantly upregulates keratinocyte FasL expression, resulting in Fas- and caspase-8-mediated keratinocyte cell death. Taken together, our data suggest that T-lymphocyte activation by drugs in TEN patients may indirectly lead to FasL-mediated keratinocyte apoptosis, via a molecular bridge involving TNF-α, IFN-γ, and iNOS.

Simultaneous modulation of COX-2, p300, Akt, and Apaf-1 signaling by melatonin to inhibit proliferation and induce apoptosis in breast cancer cells

Melatonin exhibits anti-inflammatory and anticancer effects and could be a chemopreventive and chemotherapeutic agent against cancers, but the precise mechanisms involved remain largely unresolved. In this study, we evaluated the mechanism of action of melatonin in human MDA-MB-361 breast cancer cells. Melatonin at pharmacological concentrations (10(-3)  m) significantly suppressed cell proliferation and induced apoptosis in a dose-dependent manner. The observed suppression of proliferation was accompanied by the melatonin-mediated inhibition of COX-2, p300, and NF-κB signaling. Melatonin significantly inhibited COX-2 expression and prostaglandin E(2) (PGE2) production, abrogated p300 histone acetyltransferase activity and p300-mediated NF-κB acetylation, thereby blocking NF-κB binding and p300 recruitment to COX-2 promoter. Pretreatment with a COX-2- or p300-selective inhibitor abrogated the melatonin-induced inhibition of cell proliferation, whereas PGE2 treatment or COX-2 transfection reversed the inhibition by melatonin. Moreover, melatonin markedly inhibited phosphorylation of PI3K, Akt, PRAS40, and GSK-3 proteins, thereby inactivating the PI3K/Akt signaling pathway. Pretreatment with a PI3K- or an Akt-selective inhibitor or an Akt-specific siRNA blocked the melatonin-mediated inhibition of cell proliferation. Conversely, gene delivery of a constitutively active Akt effectively reversed the inhibition by melatonin. Furthermore, melatonin induced Apaf-1 expression, triggered cytochrome C release, and stimulated caspase-3 and caspase-9 activities and cleavage, leading to an activation of the Apaf-1-dependent apoptotic pathway. Pretreatment with an Apaf-1-specific siRNA effectively attenuated the melatonin-induced apoptosis. These results therefore indicate that melatonin inhibits cell proliferation and induces apoptosis in MDA-MB-361 breast cancer cells in vitro by simultaneously suppressing the COX-2/PGE2, p300/NF-κB, and PI3K/Akt/signaling and activating the Apaf-1/caspase-dependent apoptotic pathway.

Role of the microenvironment in tumor growth and in refractoriness/resistance to anti-angiogenic therapies

Angiogenesis is critical for growth of many tumor types and the development of anti-angiogenic agents opened a new era in cancer therapy. However, similar to other anti-cancer therapies, inherent/acquired resistance to anti-angiogenic drugs may occur in cancer patients leading to disease recurrence. Recent studies in several experimental models suggest that both tumor and non-tumor (stromal) cell types may be involved in the reduced responsiveness to the treatments. The current review focuses on the role of stromal cells in tumor growth and in refractoriness to anti-VEGF treatment.

Ups and downs: the STAT1:STAT3 seesaw of Interferon and gp130 receptor signalling

Downstream of cytokine or growth factor receptors, STAT3 counteracts inflammation and promotes cell survival/proliferation and immune tolerance while STAT1 inhibits proliferation and favours innate and adaptive immune responses. STAT1 and STAT3 activation are reciprocally regulated and perturbation in their balanced expression or phosphorylation levels may re-direct cytokine/growth factor signals from proliferative to apoptotic, or from inflammatory to anti-inflammatory. Here we review the functional canonical and non-canonical effects of STAT1/3 activation and discuss the hypothesis that perturbation of their expression and/or activation levels may provide novel therapeutic strategies in different clinical settings and particularly in cancer.

Erythema multiforme and related disorders

Erythema multiforme (EM) and related disorders comprise a group of mucocutaneous disorders characterized by variable degrees of mucosal and cutaneous blistering and ulceration that occasionally can give rise to systemic upset and possibly compromise life. The clinical classification of these disorders has often been variable, thus making definitive diagnosis sometimes difficult. Despite being often caused by, or at least associated with, infection or drug therapy, the pathogenic mechanisms of these disorders remain unclear, and as a consequence, there are no evidence-based, reliably effective therapies. The present article reviews aspects of EM and related disorders of relevance to oral medicine clinical practice and highlights the associated potential etiologic agents, pathogenic mechanisms and therapies.

Inducible nitric oxide synthase and apoptosis in human B cell lymphomas

Nitric oxide synthases are isoenzymes that catalyse the synthesis of nitric oxide (NO). NO plays both pathological and physiological roles depending on its rate of synthesis and concentration in cellular source and microenvironment. Apoptosis is an important biological factor in lymphomas. This study evaluates expression of inducible nitric oxide synthase (iNOS) in human lymphomas and its relation with apoptosis. This study comprised 46 cases of B-cell lymphoma. The lymphomas were classified as 3 mantle cell, 5 marginal zone, 4 follicular, 2 Burkitt, 25 diffuse large cell, 2 anaplastic large cell, 3 lymphoblastic, 2 lymphoplasmacytic according to WHO classification of lymphoid neoplasms. Hematoxylin eosin slides of the cases were reviewed and immunoperoxidase technique was performed iNOS and Caspase monoclonal antibodies to selected sections of each case. Antigen staining was carried out with iNOS and Caspase proteins and Ultravision Polyvalent, HRP-AEC kit (Neomarkers-Biogen USA). For the evaluation of iNOS and Caspase, tumor areas with a high density of expression were chosen. Positive stained cells were counted in 5 different areas at a magnification x 40 by an Olympus B x 51 microscope in each case. The iNOS and Caspase expressions were independently recorded by four pathologists and the results were averaged. All of the cases were positive for the iNOS and Caspase. But there is not a statistically important relation between lymphoma grade and iNOS activity. We could not find a correlation between iNOS and patients age. This study reveals the capacity of B-cell neoplasms to express iNOS in situ. In conclusion, our study revealed that there is a positive relation between iNOS expression and apoptosis (p = 0.032 spearman correlation).

Can β-carotene regulate cell growth by a redox mechanism? An answer from cultured cells

Many studies suggest a protective role of beta-carotene against cancer. However, the ATBC and the CARET trials have shown that beta-carotene increases the incidence of lung cancer in heavy smokers and asbestos workers. To explain this paradox, it can be hypothesized that beta-carotene modulates intracellular redox status and through this mechanism, it affects redox-sensitive molecular pathways involved in the regulation of cell cycle progression and apoptosis. Studies conducted in cultured cells seem to confirm such a hypothesis. At low concentrations, the carotenoid may serve as an antioxidant, inhibiting free radical production, while at relatively high concentrations and/or in the presence of a chronic oxidative stress (i.e. smoke), it may behave as a prooxidant, propagating free radical-induced reactions, consuming endogenous antioxidants and inducing DNA oxidative damage. In this context, it may regulate cell growth and death by the modulation of redox-sensitive genes and transcription factors.

Different sensitivity of lamina propria T-cell subsets to nitric oxide-induced apoptosis explains immunomodulatory activity of a nitric oxide-releasing derivative of mesalamine in rodent colitis

BACKGROUND & AIMS

Uncontrolled T-cell activation plays a critical role in the pathogenesis of inflammatory bowel diseases. Therefore, pharmacological strategies directed toward restoring the normal responsiveness of the immune system could be effective in the treatment of these pathologic conditions. The addition of a nitric oxide-releasing moiety to conventional drugs, such as aspirin and other anti-inflammatory analgesic drugs, results in new chemical entities with potent immunomodulatory activities. The aim of this study was to investigate the immunomodulatory activity of a nitric oxide-releasing derivative of mesalamine (NCX-456), as compared with standard mesalamine, in 2,4,6-trinitrobenzene sulfonic acid-induced colitis in mice.

METHODS

Cells and tissues from mice with 2,4,6-trinitrobenzene sulfonic acid-induced colitis and from interleukin 10-deficient mice with spontaneous chronic colitis receiving treatment with several doses of NCX-456 or mesalamine were analyzed for morphology, cytokine production, and apoptosis.

RESULTS

NCX-456, but not mesalamine, administration resulted in a marked reduction in clinical, histological, and immunologic signs of colitis in both models. NCX-456 inhibited the release of T-helper type 1-derived cytokines and increased the release of the regulatory T cell-derived cytokines interleukin 10 and transforming growth factor beta. In vitro analyses showed that NCX-456 inhibited proliferation and caused selective apoptosis of the subset of activated lamina propria T-helper type 1 cells, whereas it was ineffective for regulatory T-cell function and survival.

CONCLUSIONS

Collectively, these data show that NCX-456 inhibits lamina propria T-helper type 1 function and stimulates the activity of interleukin 10- and transforming growth factor beta-secreting cells, thus restoring mucosal immune homeostasis and suppressing intestinal inflammation.

Modulation of TNF-α activity in tumor PC cells using anti-CD45 and anti-CD95 monoclonal antibodies

TNF-alpha is a pleiotropic cytokine produced by activated T-cytotoxic lymphocytes and NK cells that is involved in signal transduction after interacting with the appropriate cell surface receptors. The modulation of signals by TNF-alpha receptor super-family is involved in the regulation of cell activation, proliferation, differentiation and control of the cell survival including cell death by apoptosis and necrosis. We have monitored the kinetics of apoptosis/necrosis on PC cells, after TNF-alpha exposure of pre-treated cells to anti-CD95 and anti-CD45 monoclonal antibodies. The results showed that in comparison with untreated cells, TNF-alpha, after 6-24 h of incubation significantly increased apoptosis and necrosis in PC cells. These effects were significantly different in comparison to both untreated cells and cells pre-treated with anti-CD45 monoclonal antibodies. However, TNF-alpha on PC cells pre-treated with anti-CD95 monoclonal antibody significantly decreased apoptotic and necrotic form of cell death. We concluded that anti-CD45 and CD95 monoclonal antibodies modulates the effect of TNF-alpha on this cell line in vitro, and that these molecules participate in TNF-alpha cytotoxic response.

Modulation of apoptotic signalling by carotenoids in cancer cells

There is a growing body of literature on the role of beta-carotene and other carotenoids in human chronic diseases, including cancer. While epidemiological evidence shows that a high dietary intake of fruits and vegetables rich in carotenoids is associated with a reduced risk for cancer, results from intervention trials indicate that supplemental beta-carotene enhances the risk of developing lung cancer incidence and mortality among smokers. A possible mechanism which can explain the dual role of carotenoids as both beneficial and harmful agents in cancer is that their excess or deficiency may bring about changes in molecular pathways involved in apoptotic signalling. Carotenoid ability in inhibiting or in enhancing apoptosis depends on several factors: carotenoid concentration, concerted action of multiple micronutrients, cell type, and redox status. This review summarizes the available evidence for a modulatory action of carotenoids on apoptosis and focuses on the main molecular pathways involved in this process.

Combined action of extracellular signal-regulated kinase and p38 kinase rescues Molt4 T cells from nitric oxide-induced apoptotic and necrotic cell death

The mechanisms that regulate nitric oxide (NO)-induced apoptosis, especially in T cell apoptosis, are largely uncharacterized. Here, we report that protection from NO-induced cell death by phorbol 12-myristate 13-acetate (PMA) is dependent on both p38 and extracellular signal-regulated kinase (ERK) activation. Exposure of Molt4 cells to NO donor S-nitroso-N-acetyl-DL-penicillamine (SNAP) induced both apoptotic and necrotic modes of cell death along with a sustained increase in p38 kinase phosphorylation. However, the p38 inhibitor SB202190 only slightly protected Molt4 cells from NO toxicity. In contrast, PMA rapidly phosphorylated both p38 kinase and ERK, and the phosphorylation statuses were not altered in the presence of SNAP. Interestingly, although each mitogen-activated protein kinase (MAPK) inhibitor by itself had only a modest effect, the combination of inhibitors for both MAPKs almost completely abolished the protective effect of PMA. Furthermore, dominant negative or catalytically inactive variants that modulate p38 and ERK mimicked the effects of MAPK inhibitors. We located the action of p38 and ERK upstream of the p53/mitochondrial membrane potential loss and caspases cascade. Together, these findings suggest that the PMA-induced activations of ERK and p38 kinase are parallel events that are both required for inhibition of NO-induced death of Molt4 cells.

Mechanism of activation of caspase cascade during beta-carotene-induced apoptosis in human tumor cells

In this study, we examined possible mechanisms of caspase activation during carotenoid-induced apoptosis in tumor cells. We found that beta-Carotene induces apoptosis by the activation of caspase-3 in human leukemia (HL-60), colon adenocarcinoma (HT-29) as well as melanoma (SK-MEL-2) cell lines. This activation is dose dependent and follows that of caspase-8 and caspase-9. Although caspase-8 cleavage is an early event, reaching its maximum activation at 3 h, caspase-9 reaches its maximum activation only at 6 h. The addition of IETD-CHO, a caspase-8-specific inhibitor, completely prevents beta-Carotene-induced apoptosis, whereas only a partial prevention was observed in the presence of LEHD-CHO, a caspase-9-specific inhibitor. beta-Carotene activates caspase-9 via cytochrome c release from mitochondria and loss of mitochondrial membrane potential (Dym). Concomitantly, a dose-dependent decrease in the antiapoptotic protein Bcl-2 and a dose-dependent increase in the cleaved form of BID (t-BID) are observed. Moreover, NF-kB activation is involved in beta-Carotene-induced caspase cascade. These results support a pharmacological role for beta-Carotene as a candidate antitumor agent and show a possible sequence of molecular events by which this molecule may induce apoptosis in tumor cells.

Suppression of NF-kappa B survival signaling by nitrosylcobalamin sensitizes neoplasms to the anti-tumor effects of Apo2L/TRAIL

We have previously demonstrated the anti-tumor activity of nitrosylcobalamin (NO-Cbl), an analog of vitamin B12 that delivers nitric oxide (NO) and increases the expression of tumor necrosis factor-related apoptosis-inducing ligand (Apo2L/TRAIL) and its receptors in human tumors. The specific aim of this study was to examine whether NO-Cbl could sensitize drug-resistant melanomas to Apo2L/TRAIL. Antiproliferative effects of NO-Cbl and Apo2L/TRAIL were assessed in malignant melanomas and non-tumorigenic melanocyte and fibroblast cell lines. Athymic nude mice bearing human melanoma A375 xenografts were treated with NO-Cbl and Apo2L/TRAIL. Apoptosis was measured by TUNEL and confirmed by examining levels and activity of key mediators of apoptosis. The activation status of NF-kappa B was established by assaying DNA binding, luciferase reporter activity, the phosphorylation status of I kappa B alpha, and in vitro IKK activity. NO-Cbl sensitized Apo2L/TRAIL-resistant melanoma cell lines to growth inhibition by Apo2L/TRAIL but had minimal effect on normal cell lines. NO-Cbl and Apo2L/TRAIL exerted synergistic anti-tumor activity against A375 xenografts. Treatment with NO-Cbl followed by Apo2L/TRAIL induced apoptosis in Apo2L/TRAIL-resistant tumor cells, characterized by cleavage of caspase-3, caspase-8, and PARP. NO-Cbl inhibited IKK activation, characterized by decreased phosphorylation of I kappa B alpha and inhibition of NF-kappa B DNA binding activity. NO-Cbl suppressed Apo2L/TRAIL- and TNF-alpha-mediated activation of a transfected NF-kappa B-driven luciferase reporter. XIAP, an inhibitor of apoptosis, was inactivated by NO-Cbl. NO-Cbl treatment rendered Apo2L/TRAIL-resistant malignancies sensitive to the anti-tumor effects of Apo2L/TRAIL in vitro and in vivo. The use of NO-Cbl and Apo2L/TRAIL capitalizes on the tumor-specific properties of both agents and represents a promising anti-cancer combination.

Protective effect of prolactin and placental lactogen on NO-induced Nb2 lymphoma cell apoptosis

Nitric oxide (NO) is an important modulator involved in immune regulation. Here, we describe conditions under which NO-donors induce apoptosis on Nb2 lymphoma cells, as evidenced by decreased cell viability and increased hypodiploid DNA content determined by flow cytometry. In addition, DNA fragmentation typical of apoptosis was shown by agarose gel electrophoresis. This apoptosis was accompanied by a significant increase of caspase-3-like enzymatic activity. Both ovine prolactin (oPRL) and ovine placental lactogen (oPL) exerted a protective effect on the NO-donor-induced apoptosis. Furthermore, dexamethasone (Dex)-induced cell death was also associated with caspase-3-like activity and oPL had the same potency as oPRL in its protective effect on Dex-induced apoptosis of Nb2 cells.

Apoptosis: biochemical aspects and clinical implications

Apoptosis and necrosis represent two distinct types of cell death. Apoptosis possesses unique morphologic and biochemical features which distinguish this mechanism of programmed cell death from necrosis. Extrinsic apoptotic cell death is receptor-linked and initiates apoptosis by activating caspase 8. Intrinsic apoptotic cell death is mediated by the release of cytochrome c from mitochondrial and initiates apoptosis by activating caspase 3. Cancer chemotherapy utilizes apoptosis to eliminate tumor cells. Agents which bind to the minor groove of DNA, like camptothecin and Hoechst 33342, inhibit topoisomerase I, RNA polymerase II, DNA polymerase and initiate intrinsic apoptotic cell death. Hoechst 33342-induced apoptosis is associated with disruption of TATA box binding protein/TATA box complexes, replication protein A/single-stranded DNA complexes, topoisomerase I/DNA cleavable complexes and with an increased intracellular concentration of E2F-1 transcription factor and nitric oxide concentration. Nitric oxide and transcription factor activation or respression also regulate the two apoptotic pathways. Some human diseases are associated with excess or deficient rates of apoptosis, and therapeutic strategies to regulate the rate of apoptosis include inhibition or activation of caspases, mRNA antisense to reduce anti-apoptotic factors like Bcl-2 and survivin and recombinant TRAIL to activate pro-apoptotic receptors, DR4 and DR5.

Interaction between nitric oxide and subsets of human T lymphocytes with differences in glutathione metabolism

Nitric oxide (NO) modulates human T-lymphocyte responses through several mechanisms. In the current study we show that interactions between NO and glutathione (GSH) metabolism are related to the selective persistent inhibition of interferon-gamma (IFN-gamma) production by NO, which we previously identified. T cells were exposed to NO using the NO-donor compound Spermine-nonoate (Sper) and activated using anti-CD3 plus anti-CD28 monoclonal antibodies. Persistent inhibition of IFN-gamma by Sper was prevented by addition of the GSH precursor l-cysteine, which inhibits Sper induced GSH depletion. Subsets of cells were either susceptible (GSH(low)) or resistant (GSH(high)) to NO-induced GSH depletion. The GSH(low) subset was characterized by enhanced numbers of CD4+ cells, reduced numbers of activated cells as characterized by CD25 and CD69, and reduced numbers of memory (CD45RO+) cells relative to the GSH(high) population. Rather than directly affecting susceptibility to NO, these surface markers reflected different expression patterns. Particularly, the GSHlow subset was further characterized by decreased activity of the GSH synthesis related enzymes multi-drug resistance related protein (MRP)-1 and gamma-glutamyltranspeptidase (gamma-GT). Blocking gamma-GT, using acivicin was shown to exacerbate NO-induced GSH depletion and NO-induced apoptosis. Since NO induced apoptosis selectively affects IFN-gamma production these findings implicate GSH metabolism in the modulation and maintenance of the T helper (Th)1/Th2 balance.

With a little help from your friends: cells don't die alone

Phagocytes have long been known to engulf and degrade apoptotic cells. Recent studies in mammals and the nematode Caenorhabditis elegans have shed some light on the conserved molecular mechanisms involved in this process. A series of results now challenge the traditional view of phagocytes as simply scavengers, 'cleaning up' after apoptosis to prevent inflammatory responses, and hence tissue damage. Instead, they suggest that phagocytes are active in the induction and/or execution of apoptosis in target cells.

Nitric oxide induces apoptosis in NALM-6, a leukaemia cell line with low cyclin E protein levels

Intracellular nitric oxide levels may differ in resting and stimulated cells and contribute to the regulation of cell survival and proliferation through a variety of mechanisms and effects. We exposed two B-cell lines to a range of S-nitroso-N-acetyl-D,L-penicillamine (SNAP) concentrations in order to examine their susceptibility to exogenous nitric oxide and the participation of nitric oxide as modulator of cell proliferation. Although both FLEB and NALM-6 decreased their levels of thymidine incorporation, only NALM-6 cells were induced to undergo G1 arrest, phosphatidyl serine exposure and DNA fragmentation when cultured in the presence of 250 microm SNAP. This higher sensitivity of NALM-6 coincided with initially low cyclin E protein levels which were increased 7.8-fold after culture for 24 h with 250 microm SNAP. In contrast, there was no difference in cyclins A and D3, Bcl-2 and actin levels, neither at the beginning nor at the end of the 24 h culture. Our study reveals that FLEB and NALM-6 exhibit different response to the same concentration of nitric oxide, that nitric oxide can simultaneously induce cell cycle alterations and apoptosis, and further suggests an association between these two processes, with the involvement of cell cycle regulatory molecules.

Microencapsulated iNOS-expressing cells cause tumor suppression in mice

Macrophages can kill tumor cells by releasing high levels of nitric oxide (NO) and related reactive nitrogen species such as nitroxyl and peroxynitrite, after up-regulation of expression of the inducible nitric oxide synthase gene (iNOS). In this paper we describe two novel human cell lines that are capable of expressing high levels of iNOS under the control of analogues of either the insect hormone ecdysone or tetracycline. We have entrapped these iNOS-expressing cells within a semipermeable alginate-poly-L-lysine membrane as a means of delivery to tumor sites in a nude mouse model. These encapsulated cells can be induced to generate sustainable high concentrations NO and reactive nitrogen species at tumor sites after treatment either with ponasterone A or muristerone A or with doxycycline. Delivery of these iNOS-expressing cells to tumors formed from human ovarian cancer SKOV-3 cells results in 100% killing, whereas treatment of tumors formed from human colon cancer DLD-1 cells results in 54% killing. We show that in these iNOS-expressing cells, tumor killing is associated with concomitant up-regulation of the Fas/FasL proteins.

TRAIL, FasL and a blocking anti-DR5 antibody augment paclitaxel-induced apoptosis in human non-small-cell lung cancer

Lung carcinoma is one of the most frequent causes of malignancy-related mortality in the world. Paclitaxel (PA) is an antineoplastic agent used in the treatment of non-small-cell lung cancer (NSCLC) and possesses a single-agent response rate approaching 25%. PA kills tumor cells by inducing both cellular necrosis and apoptosis. Fas and Trail receptors (DR4 and DR5) are TNF family members and act as death signal transduction proteins in the apoptosis cascade. Despite the importance of PA in lung cancer treatment, the function of Fas, DR4 and DR5 in PA-induced apoptosis, as well as the effect of their respective ligands FasL and TRAIL alone or in combination with PA, remains poorly understood. We show here that 10 microM PA induces a significant 10- to 57-fold increase in primary lung cancer cell apoptosis and is associated with 20-215% increases in caspase-3 activity in various NSCLC cell types. All the lung cancer cells express Fas, FasL, DR4 and DR5; however PA did not significantly modify their levels. We provide here the first time evidence that TRAIL is a potent inducer of apoptosis in multiple NSCLC cell lines. Noticeably, CH11, the Fas receptor cross-linking and the antagonistic anti-DR5 antibody enhance considerably the spontaneous apoptotic rate in 3 out of 5 cell types. The combination treatments, FasL+PA, TRAIL+PA or PA+anti-DR5 antibody, greatly enhance PA-apoptotic effect in most cell lines. These data suggest that the use of new combination treatment with PA and ligands targeting Fas or TRAIL receptors would be particularly efficacious.

Nitric oxide-induced apoptosis in tumor cells

Nitric oxide (NO), an important molecule involved in neurotransmission, vascular homeostasis, immune regulation, and host defense, is generated from a guanido nitrogen of L-arginine by the family of NO synthase enzymes. Large amounts of NO produced for relatively long periods of time (days to weeks) by inducible NO synthase in macrophages and vascular endothelial cells after challenge with lipopolysaccharide or cytokines (such as interferons, tumor necrosis factor-alpha, and interleukin-1), are cytotoxic for various pathogens and tumor cells. This cytotoxic effect against tumor cells was found to be associated with apoptosis (programmed cell death). The mechanism of NO-mediated apoptosis involves accumulation of the tumor suppressor protein p53, damage of different mitochondrial functions, alterations in the expression of members of the Bcl-2 family, activation of the caspase cascade, and DNA fragmentation. Depending on the amount, duration, and the site of NO production, this molecule may not only mediate apoptosis in target cells but also protect cells from apoptosis induced by other apoptotic stimuli. In this review, we will concentrate on the current knowledge about the role of NO as an effector of apoptosis in tumor cells and discuss the mechanisms of NO-mediated apoptosis.

Evidence for involvement of c-Src in the anti-apoptotic action of nitric oxide in serum-deprived RINm5F cells

The mechanism by which nitric oxide (NO) protects from apoptosis is a matter of debate. We have shown previously that phosphorylation of tyrosine residues participates in the protection from apoptosis in insulin-producing RINm5F cells (Inorg. Chem. Commun. 3 (2000) 32). Since NO has been reported to activate the tyrosine kinase c-Src and this kinase is involved in the activation of protein kinase G (PKG) in some cell systems, we aimed at studying the contribution of c-Src and PKG systems in anti-apoptotic actions of NO in serum-deprived RINm5F cells. Here we report that exposure of serum-deprived cells to 10 microM DETA/NO results in protection from degradation of the anti-apoptotic protein Bcl-2, together with a reduction of cytochrome c release from mitochondria and caspase-3 inhibition. Studies with the inhibitors ODQ and KT-5823 revealed that these actions are dependent on both activation of guanylate cyclase and PKG. DETA/NO was also able to induce autophosphorylation and activation c-Src protein both in vivo and in vitro and active c-Src was able to induce tyrosine phosphorylation of Bcl-2 in vitro. The c-Src kinase inhibitor PP1 abrogated the actions of DETA/NO on cGMP formation, PKG activation, caspase activation, cytochrome c release from mitochondria, and Bcl-2 phosphorylation and degradation in serum-deprived cells. We thus propose that activation of c-Src is an early step in the chain of events that signal cGMP-dependent anti-apoptotic actions of NO in mitocohondria.

Activation of the nitric oxide synthase pathway represents a key component of tumor necrosis factor-related apoptosis-inducing ligand-mediated cytotoxicity on hematologic malignancies

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induced both cytotoxic (apoptosis) and cytostatic (cell cycle perturbation) effects on the human myeloid K562 cell line. TRAIL stimulated caspase 3 and nitric oxide synthase (NOS) activities, and both pathways cooperate in mediating inhibition of K562 survival/growth. This was demonstrated by the ability of z-VAD-fmk, a broad inhibitor of effector caspases, and N-nitro-L-arginine methyl ester (L-NAME), an NOS pharmacologic inhibitor, to completely (z-VAD-fmk) or partially (L-NAME) suppress the TRAIL-mediated inhibitory activity. Moreover, z-VAD-fmk was able to block TRAIL-mediated apoptosis and cell cycle abnormalities and increase of NOS activity. The addition of the NO donor sodium nitroprusside (SNP) to K562 cells reproduced the cytostatic effect of TRAIL without inducing apoptosis. When TRAIL was associated to SNP, a synergistic increase of apoptosis and inhibition of clonogenic activity was observed in K562 cells as well as in other myeloblastic (HEL, HL-60), lymphoblastic (Jurkat, SupT1), and multiple myeloma (RPMI 8226) cell lines. Although SNP greatly augmented TRAIL-mediated antileukemic activity also on primary leukemic blasts, normal erythroid and granulocytic cells were less sensitive to the cytotoxicity mediated by TRAIL with or without SNP. These data indicate that TRAIL promotes cytotoxicity in leukemic cells by activating effector caspases, which directly lead to apoptosis and stimulate NO production, which mediates cell cycle abnormalities. Both mechanisms seem to be essential for TRAIL-mediated cytotoxicity.

The regulatory role of nitric oxide in apoptosis

Nitric oxide (NO) is a multi-faceted molecule with dichotomous regulatory roles in many areas of biology. The complexity of its biological effects is a consequence of its numerous potential interactions with other molecules such as reactive oxygen species (ROS), metal ions, and proteins. The effects of NO are modulated by both direct and indirect interactions that can be dose-dependent and cell-type specific. For example, in some cell types NO can promote apoptosis, whereas in other cells NO inhibits apoptosis. In hepatocytes, NO can inhibit the main mediators of cell death-caspase proteases. Moreover, low physiological concentrations of NO can inhibit apoptosis, but higher concentrations of NO may be toxic. High NO concentrations lead to the formation of toxic reaction products like dinitrogen trioxide or peroxynitrite that induce cell death, if not by apoptosis, then by necrosis. Long-term exposure to nitric oxide in certain conditions like chronic inflammatory states may predispose cells to tumorigenesis through DNA damage, inhibition of DNA repair, alteration in programmed cell death, or activation of proliferative signaling pathways. Understanding the regulatory mechanisms of NO in apoptosis and carcinogenesis will provide important clues to the diagnosis and treatment of tissue damage and cancer. In this article we have reviewed recent discoveries in the regulatory role of NO in specific cell types, mechanisms of pro-apoptotic and anti-apoptotic induction by NO, and insights into the effects of NO on tumor biology.

[Pro- and anti-apoptotic role of nitric oxide, NO]

NO displays both pro- and anti-apoptotic properties. The parameters governing these effects begin to be elucidated. Among these figure the nature of the cells, their redox state, the flow and concentration of NO, its possibility to react with superoxide generated at the level of mitochondria. The targets of NO include molecules involved in DNA repair, such as PARP, the DNA-dependent protein kinase (DNA-PK) and p53 which control the transcription of various genes involved in the apoptotic process (bax, cdk inhibitors), and the proteasome which control the degradation of several apoptotic proteins. The inhibition by NO of caspases through S-nitrosylation of their active sites provides a rationale for our understanding of the anti-apoptotic effect of NO, but other mechanisms are involved, such as a regulation of the mitochondrial permeability. A better knowledge of the various steps of the apoptotic process that are affected by NO would allow the design of new pharmacological tools.

Inhibition of nitric-oxide-mediated apoptosis in Jurkat leukemia cells despite cytochrome c release

We have recently shown that nitric-oxide (NO)-induced apoptosis in Jurkat human leukemia cells requires degradation of mitochondria phospholipid cardiolipin, cytochrome c release, and activation of caspase-9 and caspase-3. Moreover, an inhibitor of lipid peroxidation, Trolox, suppressed apoptosis in Jurkat cells induced by NO donor glycerol trinitrate. Here we demonstrate that this antiapoptotic effect of Trolox occurred despite massive release of the mitochondrial protein cytochrome c into the cytosol and mitochondrial damage. Incubation with Trolox caused a profound reduction of intracellular ATP concentration in Jurkat cells treated by NO. Trolox prevented cardiolipin degradation and caused its accumulation in Jurkat cells. Furthermore, Trolox markedly downregulated the NO-mediated activation of caspase-9 and caspase-3. Caspase-9 is known to be activated by released cytochrome c and together with caspase-3 is considered the most proximal to mitochondria. Our results suggest that the targets of the antiapoptotic effect of Trolox are located downstream of the mitochondria and that caspase activation and subsequent apoptosis could be blocked even in the presence of cytochrome c released from the mitochondria.

Caspases: conductors of the cell death machinery in lymphoma cells

The present review focuses on recent insights into the regulation of caspases by other components of the apoptotic pathway, including the mechanisms by which caspase activation influence the death of lymphoma cells. In the light of our recent findings and similar observations of other investigators, it is likely that lymphoma cells possess the complete caspase machinery required for the apoptotic process. Inhibition of caspases activation appears as a potential mechanism to explain apoptotic defects of malignant B-cells, and thus may constitute the basis for new cancer therapies.

Sodium nitroprusside enhances TRAIL-induced apoptosis via a mitochondria-dependent pathway in human colorectal carcinoma CX-1 cells

The tumor necrosis factor-related apoptosis-inducing ligand (TRAIL, Apo-2L) is a recently characterized member of the family of programmed cell death-inducing ligands that includes TNF-alpha and CD95L (FasL). It is well known that TRAIL binds to the death signaling receptors, DR4 and DR5, and initiates the TRAIL death pathway. Activation of this pathway, mediated through a caspase cascade, causes apoptosis. In this study, we hypothesized that oxidative stress facilitates TRAIL-induced apoptosis by promoting caspase activity through cytochrome c release from mitochondria. Human colorectal carcinoma CX-1 cells were treated with various concentrations of TRAIL (12.5-200 ng/ml) and/or sodium nitroprusside (SNP; 0.03-1 mM) for 12 h. SNP, a nitric oxide donor, which had little toxic effect by itself, enhanced TRAIL-induced cytotoxicity. For example, TRAIL-induced apoptosis (200 ng/ml) was increased by a factor of 2.5-fold in the presence of 1 mM SNP. The combined treatment also caused an increase in cytochrome c release, caspase-3 activity, and PARP cleavage. Overexpression of Bcl-2 completely blocked the SNP-promoting effects, but only moderately inhibited TRAIL-induced apoptosis. Similar results were observed in the presence of hydrogen peroxide or peroxynitrite. Taken together, the present studies suggest that SNP enhances TRAIL-induced cytotoxicity by facilitating the mitochondria-mediated caspase signal transduction pathway.

Effects and expression of TRAIL and its apoptosis-promoting receptors in human pancreatic cancer

Pancreatic cancer cells are usually resistant to apoptosis mediated by tumor necrosis factor (TNF)-alpha or FasL, and their toxicity towards normal cells hampers their application for therapeutic use. TNF-related apoptosis-inducing ligand (TRAIL), a novel member of the TNF family, triggers apoptosis in a variety of malignant cells, but exhibits less cytotoxicity in normal cells. To investigate the therapeutic potential of TRAIL, we analyzed the expression of TRAIL and its apoptosis-inducing receptors (DR4 and DR5) in the normal and cancerous human pancreas, and the sensitivity of pancreatic cancer cells to TRAIL cytotoxicity. TRAIL, DR4 and DR5 mRNA levels were concomitantly increased in pancreatic cancers compared with normal controls (P<0.01), and there were positive correlations between the expression levels of TRAIL and DR4, TRAIL and DR5 and between DR4 and DR5 mRNA (r=0.85, r=0.87, r=0.91; P<0.01). Immunostaining revealed the presence of the corresponding proteins frequently within the same cancer cells. In five pancreatic cancer cell lines, TRAIL, DR4 and DR5 mRNA expression was detectable at various levels. However, independent of the presence of DR4 and DR5, TRAIL cytotoxicity assays revealed that pancreatic cancer cells showed a significantly lower sensitivity (LD(50)>85 ng/ml) to TRAIL treatment than Jurkat T lymphoma cells (LD(50)=7.2 ng/ml). These findings show that pancreatic cancers are insensitive towards TRAIL-mediated apoptosis despite expression of TRAIL and its receptors, suggesting the presence of mediators which inhibit the TRAIL cell-death-inducing pathway in pancreatic cancer cells.

Mechanisms involved in the pro- and anti-apoptotic role of NO in human leukemia

Nitric oxide (NO) exerts contrasting effects on apoptosis, depending on its concentration, flux and cell type. In some situations, NO activates the transduction pathways leading to apoptosis, whereas in other cases NO protects cells against spontaneous or induced apoptosis. The redox state of the cells appears to be a crucial parameter for the determination of the ultimate action of NO on cell multiplication and survival. Apoptosis is mostly associated with the delivery of NO by chemical donors and with myelomonocytic cells, whereas antiapoptotic effects seem to be related to the endogenous production of NO by NO synthases and is observed more frequently in cells of the B lymphocyte lineage. Pro-apoptotic effects are often observed when NO reacts with superoxide to produce the highly toxic peroxynitrite. Through the induction of damages to DNA, NO stimulates the expression of enzymes and transcription factors involved in DNA repair and modulation of apoptosis, such as the tumor suppressor p53. The latter molecule transactivates the expression of pro-apoptotic genes, such as bax, and that of the cyclin-dependent kinase inhibitor p21, whereas it down-regulates the expression of the anti-apoptotic protein bcl-2. On the other hand, NO inactivates caspases through oxidation and S-nitrosylation of the active cystein, providing an efficient means to block apoptosis. Other protective effects of NO on apoptosis rely on the stimulation of cGMP-dependent protein kinase (PKG), modulation of the members of the bcl-2/bax family that control the mitochondrial pore transition permeability, induction of the heat shock protein HSP 70 and interaction with the ceramide pathway. A defect in the apoptotic process contributes to the accumulation of tumoral cells in leukemia, notably in B-CLL. A better knowledge of the targets of NO would provide efficient means to control cell apoptosis, and hence would possibly lead to the development of new therapeutic approaches for diseases where an alteration of apoptosis is involved.

Poliovirus induces apoptosis in the human U937 promonocytic cell line

The human promonocytic U937 cell line, which is moderately susceptible to poliovirus infection, has been used to investigate the induction of apoptosis by this virus. Infection of U937 cells with poliovirus induces morphological changes typical of apoptosis. Poliovirus-resistant U937 cells (PRU) have been isolated that are resistant to apoptosis induced by poliovirus, but that undergo apoptosis after treatment with TNF plus cycloheximide. Despite the fact that poliovirus triggers nitric oxide production in U937 cells, the inhibitor of inducible nitric oxide (NO) synthase, N(omega)-monomethyl-l-arginine, did not hinder apoptosis after infection, suggesting that NO does not play a direct role in this process. Finally, poliovirus infection of U937 cells led to the cleavage of pro-caspase-3 and poly(ADP-ribose)polymerase, indicating the activation of the CPP32 ICE-like cysteine protease in the induction of apoptosis. Our findings suggest that cellular death takes place in U937 cells productively infected by poliovirus as a result of apoptosis and involves caspase activation.

Retinoic acid-mediated enhancement of the cholinergic/neuronal nitric oxide synthase phenotype of the medial septal SN56 clone: establishment of a nitric oxide-sensitive proapoptotic state

It is unclear what mechanisms lead to the degeneration of basal forebrain cholinergic neurons in Alzheimer's or other human brain diseases. Some brain cholinergic neurons express neuronal nitric oxide (NO) synthase (nNOS), which produces a free radical that has been implicated in some forms of neurodegeneration. We investigated nNOS expression and NO toxicity in SN56 cells, a clonal cholinergic model derived from the medial septum of the mouse basal forebrain. We show here that, in addition to expressing choline acetyltransferase (ChAT), SN56 cells express nNOS. Treatment of SN56 cells with retinoic acid (RA; 1 microM) for 48 h increased ChAT mRNA (+126%), protein (+88%), and activity (+215%) and increased nNOS mRNA (+98%), protein (+400%), and activity (+15%). After RA treatment, SN56 cells became vulnerable to NO excess generated with S-nitro-N-acetyl-DL-penicillamine (SNAP) and exhibited increased nuclear DNA fragmentation that was blocked with a caspase-3 inhibitor. Treatment with dexamethasone, which largely blocked the RA-mediated increase in nNOS expression, or inhibition of nNOS activity with methylthiocitrulline strongly potentiated the apoptotic response to SNAP in RA-treated SN56 cells. Caspase-3 activity was reduced when SNAP was incubated with cells or cell lysates, suggesting that NO can directly inhibit the protease. Thus, whereas RA treatment converts SN56 cells to a proapoptotic state sensitive to NO excess, endogenously produced NO appears to be anti-apoptotic, possibly by tonically inhibiting caspase-3.

Thymic dendritic cells express inducible nitric oxide synthase and generate nitric oxide in response to self- and alloantigens

Thymocytes maturing in the thymus undergo clonal deletion/apoptosis when they encounter self- or allo-Ags presented by dendritic cells (DCs). How this occurs is a matter of debate, but NO may play a role given its ability of inducing apoptosis of these cells. APC (a mixed population of macrophages (Mphi) and DCs) from rat thymus expressed high levels of inducible NO synthase (iNOS) and produced large amounts of NO in basal conditions whereas iNOS expression and NO production were very low in thymocytes. Analysis by FACS and by double labeling of cytocentrifuged preparations showed that DCs and MPhi both express iNOS within APC. Analysis of a purified preparation of DCs confirmed that these cells express high levels of iNOS and produce large amounts of NO in basal conditions. The capacity of DCs to generate NO was enhanced by exposure to rat albumin, a self-protein, and required a fully expressed process of Ag internalization, processing, and presentation. Peptides derived from portions of class II MHC molecules up-regulate iNOS expression and NO production by DCs as well, both in self and allogeneic combinations, suggesting a role of NO in both self and acquired tolerance. We also found that NO induced apoptosis of rat double-positive thymocytes, the effect being more evident in anti-CD3-stimulated cells. Altogether, the present findings might suggest that DC-derived NO is at least one of the soluble factors regulating events, in the thymus, that follow recognition of self- and allo-Ags.

Paclitaxel-induced apoptosis in non-small cell lung cancer cell lines is associated with increased caspase-3 activity

OBJECTIVE

Our objective was to determine whether paclitaxel-induced apoptosis in human lung cancer cells is Fas dependent.

METHODS

Human lung cancer cell lines were evaluated for morphologic evidence of apoptosis, DNA fragmentation (TUNEL positivity), and caspase-3 activation after paclitaxel treatment. Human lung adenocarcinoma, squamous cell carcinoma, undifferentiated lung carcinoma, and bronchoalveolar carcinoma cell lines were each cultured in 10 micromol/L paclitaxel.

RESULTS

After 24 hours of culture in paclitaxel, a 22% to 69% increase in the number of apoptotic cells was evident by means of methylene blue-azure A-eosin staining with characteristic blebbing and nuclear condensation. TUNEL assay also confirmed an increase of 19.9% to 73.0% of cells with nuclear fragmentation. Caspase-3 activity, assayed by Z-DEVD cleavage, increased from 20% to 215% (P <.05). ZB4, an antagonistic anti-Fas antibody, did not block paclitaxel induction of caspase-3 activity (155.8 vs 165.8 U, not significant). Apoptotic morphologic changes were inhibited in cells cultured in the presence of paclitaxel and Ac-DEVD-CHO, a caspase-3 inhibitor.

CONCLUSIONS

Paclitaxel induces apoptosis in lung cancer cell lines, as assessed by a consistent increase in caspase-3 activity, DNA laddering, and characteristic morphologic changes. Paclitaxel-induced apoptosis in human lung cancer cells is associated with caspase-3 activation but is not Fas dependent.

Activated macrophages direct apoptosis and suppress mitosis of mesangial cells

During inflammation in the glomerulus, the complement of resident myofibroblast-like mesangial cells is regulated by mitosis and apoptosis, but the cellular mechanisms controlling the size of mesangial cell populations have remained obscure. Prompted by studies of development, we sought evidence that macrophages regulate mesangial cell number. Rat bone marrow-derived macrophages primed with IFN-gamma then further activated in coculture with LPS or TNF-alpha elicited a 10-fold induction of rat mesangial cell apoptosis and complete suppression of mitosis, effects inhibitable by the NO synthase inhibitors L-monomethyl arginine and L-N(6)-(1-iminoethyl) lysine dihydrochloride. Complete dependence upon macrophage-derived NO was observed in comparable experiments employing activated bone marrow macrophages from wild-type and NO synthase 2(-/-) mice. Nevertheless, when mesangial cells were primed with IFN-gamma plus TNF-alpha, increased induction by activated macrophages of mesangial apoptosis exhibited a NO-independent element. The use of gld/gld macrophages excluded a role for Fas ligand in this residual kill, despite increased expression of Fas and increased susceptibility to soluble Fas ligand exhibited by cytokine-primed mesangial cells. Finally, activated macrophages isolated from the glomeruli of rats with nephrotoxic nephritis also induced apoptosis and suppressed mitosis in mesangial cells by an L-monomethyl arginine-inhibitable mechanism. These data demonstrate that activated macrophages, via the release of NO and other mediators, regulate mesangial cell populations in vitro and may therefore control the mesangial cell complement at inflamed sites.

Nitric oxide synthase in toxic epidermal necrolysis and Stevens-Johnson syndrome

Toxic epidermal necrolysis and Stevens-Johnson syndrome are severe cutaneous drug reactions of unknown mechanism. Nitric oxide can cause apoptosis and necrosis. The inducible form of nitric oxide synthase generates large amounts of nitric oxide and has been described in human skin. We propose that a large burst of nitric oxide in toxic epidermal necrolysis and Stevens-Johnson syndrome may cause the epidermal apoptosis and necrosis. Skin biopsies were taken from seven patients with actively progressing Stevens-Johnson syndrome or toxic epidermal necrolysis. Expression of inducible nitric oxide synthase was examined by reverse transcription-polymerase chain reaction and by immunoperoxidase staining for inducible nitric oxide synthase protein. Messenger RNA for inducible nitric oxide synthase was detected by reverse transcription-polymerase chain reaction and confirmed by the sequencing of polymerase chain reaction products. Strong staining for inducible nitric oxide synthase was observed in inflammatory cells in the lower epidermis and upper dermis. Diffuse, weaker staining was observed in keratinocytes. Expression of inducible nitric oxide synthase is consistent with the hypothesis that nitric oxide mediates the epidermal necrosis in toxic epidermal necrolysis and provides a potential target for therapeutic intervention.

p53 accumulation in apoptotic macrophages is an energy demanding process that precedes cytochrome c release in response to nitric oxide

Apoptosis in response to stress signals activates effector caspases known to be regulated by the release of cytochrome c (Cyt c) from mitochondria and the subsequent ATP-dependent activation of the death regulator apoptotic protease-activating factor 1 (Apaf-1). Experiments were carried out to determine whether the release of Cyt c is evoked by NO. in RAW 264.7 macrophages and to position signaling components relative to mitochondria. S-nitrosoglutathione and spermine-NO caused a fast p53 accumulation, followed by Bcl-xL downregulation, Cyt c release, and caspase activation. These alterations were absent in p53 antisense expressing macrophages (R delta p53asn-11). In Bcl-2 overexpressing cells (Rbcl2-14) Cyt c relocation and caspase activation were abrogated although p53 accumulation remained intact. The use of caspase inhibitors revealed Cyt c release and decreased Bcl-xL expression to be caspase independent. ATP-depleted cells showed a shift from apoptosis towards necrosis and no p53 accumulation or caspase activation upon NO. addition. Conclusively, NO.-mediated apoptosis in macrophages is entirely controlled by the mitochondrial pathway with the implication that Cyt c relocation demands p53 accumulation. Moreover, pulse-chase-experiments in combination with the ATP-depletion protocol identified p53 accumulation and stabilization as an energy requiring process. This allowed to dissect two ATP-dependent steps, one is in association with Apaf-1 formation, while the other resides in p53 accumulation.

NO induces a cGMP-independent release of cytochrome c from mitochondria which precedes caspase 3 activation in insulin producing RINm5F cells

Exposure of RINm5F cells to interleukin-1beta and to several chemical NO donors such as sodium nitroprusside (SNP), SIN-1 and SNAP induce apoptotic events such as the release of cytochrome c from mitochondria, caspase 3 activation, Bcl-2 downregulation and DNA fragmentation. SNP exposure led to transient activation of soluble guanylate cyclase (sGC) and prolonged protein kinase G (PKG) activation but apoptotic events were not attenuated by inhibition of the sGC/PKG pathway. Prolonged activation of the cGMP pathway by exposing cells to the dibutyryl analogue of cGMP for 12 h induced both apoptosis and necrosis, a response that was abolished by the PKG inhibitor KT5823. These results suggest that NO-induced apoptosis in the pancreatic beta-cell line is independent of acute activation of the cGMP pathway.

Bcl-2 and Bcl-X(L) block thapsigargin-induced nitric oxide generation, c-Jun NH(2)-terminal kinase activity, and apoptosis

The proteins Bcl-2 and Bcl-X(L) prevent apoptosis, but their mechanism of action is unclear. We examined the role of Bcl-2 and Bcl-X(L) in the regulation of cytosolic Ca(2+), nitric oxide production (NO), c-Jun NH(2)-terminal kinase (JNK) activation, and apoptosis in Jurkat T cells. Thapsigargin (TG), an inhibitor of the endoplasmic reticulum-associated Ca(2+) ATPase, was used to disrupt Ca(2+) homeostasis. TG acutely elevated intracellular free Ca(2+) and mitochondrial Ca(2+) levels and induced NO production and apoptosis in Jurkat cells transfected with vector (JT/Neo). Buffering of this Ca(2+) response with 1, 2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetra(acetoxymethyl) ester (BAPTA-AM) or inhibiting NO synthase activity with N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME) blocked TG-induced NO production and apoptosis in JT/Neo cells. By contrast, while TG produced comparable early changes in the Ca(2+) level (i.e., within 3 h) in Jurkat cells overexpressing Bcl-2 and Bcl-X(L) (JT/Bcl-2 or JT/Bcl-X(L)), NO production, late (36-h) Ca(2+) accumulation, and apoptosis were dramatically reduced compared to those in JT/Neo cells. Exposure of JT/Bcl-2 and JT/Bcl-X(L) cells to the NO donor, S-nitroso-N-acetylpenacillamine (SNAP) resulted in apoptosis comparable to that seen in JT/Neo cells. TG also activated the JNK pathway, which was blocked by L-NAME. Transient expression of a dominant negative mutant SEK1 (Lys-->Arg), an upstream kinase of JNK, prevented both TG-induced JNK activation and apoptosis. A dominant negative c-Jun mutant also reduced TG-induced apoptosis. Overexpression of Bcl-2 or Bcl-X(L) inhibited TG-induced loss in mitochondrial membrane potential, release of cytochrome c, and activation of caspase-3 and JNK. Inhibition of caspase-3 activation blocked TG-induced JNK activation, suggesting that JNK activation occurred downstream of caspase-3. Thus, TG-induced Ca(2+) release leads to NO generation followed by mitochondrial changes including cytochrome c release and caspase-3 activation. Caspase-3 activation leads to activation of the JNK pathway and apoptosis. In summary, Ca(2+)-dependent activation of NO production mediates apoptosis after TG exposure in JT/Neo cells. JT/Bcl-2 and JT/Bcl-X(L) cells are susceptible to NO-mediated apoptosis, but Bcl-2 and Bcl-X(L) protect the cells against TG-induced apoptosis by negatively regulating Ca(2+)-sensitive NO synthase activity or expression.