Recognition of apoptotic cells by macrophages activates the peroxisome proliferator-activated receptor-gamma and attenuates the oxidative burst.

It is appreciated that phagocytosis of apoptotic cells (AC) is an immunological relevant process that shapes the pro- versus anti-inflammatory macrophage phenotype. It was our intention to study the respiratory burst, a prototype marker of macrophage activation, under the impact of AC. Following incubation of RAW264.7 macrophages with AC, we noticed attenuated production of reactive oxygen species (ROS) in response to PMA treatment, and observed a correlation between attenuated ROS formation and suppression of protein kinase Calpha (PKCalpha) activation. EMSA analysis demonstrated an immediate activation of peroxisome proliferator-activated receptor-gamma (PPARgamma) following supplementation of AC to macrophages. In macrophages carrying a dominant-negative PPARgamma mutant, recognition of AC no longer suppressed PKCalpha activation, and the initial phase of ROS formation was largely restored. Interference with actin polymerization and transwell experiments suggest that recognition of AC by macrophages suffices to attenuate the early phase of ROS formation that is attributed to PPARgamma activation.

Activation of PPARgamma is not involved in butyrate-induced epithelial cell differentiation.

Histone deacetylase-inhibitors affect growth and differentiation of intestinal epithelial cells by inducing expression of several transcription factors, e.g. Peroxisome proliferator-activated receptor gamma (PPARgamma) or vitamin D receptor (VDR). While activation of VDR by butyrate mainly seems to be responsible for cellular differentiation, the activation of PPARgamma in intestinal cells remains to be elucidated. The aim of this study was to determine the role of PPARgamma in butyrate-induced cell growth inhibition and differentiation induction in Caco-2 cells. Treatment with PPARgamma ligands ciglitazone and BADGE (bisphenol A diglycidyl) enhanced butyrate-induced cell growth inhibition in a dose- and time-dependent manner, whereas cell differentiation was unaffected after treatment with PPARgamma ligands rosiglitazone and MCC-555. Experiments were further performed in dominant-negative PPARgamma mutant cells leading to an increase in cell growth whereas butyrate-induced cell differentiation was again unaffected. The present study clearly demonstrated that PPARgamma is involved in butyrate-induced inhibition of cell growth, but seems not to play an essential role in butyrate-induced cell differentiation.

Transcription factors p53 and HIF-1alpha as targets of nitric oxide.

It is widely recognized that the production of nitric oxide (NO) from L-arginine metabolism is an essential determinate of diverse signalling cascades throughout the body, with a major impact during nonspecific host defence. Biological actions of NO and derived species comprise physiological as well as pathological entities, with an impressive and steadily growing number of signalling pathways and/or protein targets being involved. It is now appreciated that NO not only acts as an effector molecule but also as an autocrine as well as paracrine modulator of rapid and delayed cellular responses. Among multiple targets the tumour suppressor p53 and the hypoxia inducible factor-1alpha (HIF-1alpha) emerged. Accumulation of p53 in response to NO delivery may account for an interference in cell cycle progression and/or initiation of apoptosis that is found in close correlation with inducible NO synthase (NOS) expression. Quite similarly, accumulation of HIF-1alpha not only occurs during hypoxia, but also under conditions of NO delivery, thus mimicking a situation of reduced oxygen availability. Interestingly, p53 and HIF-1alpha share regulatory elements that cause protein stabilization in part as a result of impaired ubiquitin-evoked protein degradation. Here, we summarize current knowledge on the impact of NO on p53- and HIF-1alpha-stabilization and we will discuss pathophysiological consequences. These examples may help to shape and refine current concepts of NO action with an emphasis on transcription factor regulation.

Delayed activation of PPARgamma by LPS and IFN-gamma attenuates the oxidative burst in macrophages.

Desensitization of macrophages is important during the development of sepsis. It was our intention to identify mechanisms that promote macrophage deactivation upon contact with endotoxin (LPS) and interferon-gamma (IFN-gamma) in vitro. Macrophage activation was achieved with 12-O-tetradecanoylphorbol 13-acetate (TPA), and the oxidative burst (i.e., oxygen radical formation) was followed by oxidation of the redox-sensitive dyes hydroethidine and dichlorodihydrofluorescein diacetate. Prestimulation of macrophages for 15 h with a combination of LPS/IFN-gamma attenuated oxygen radical formation in response to TPA. Taking the anti-inflammatory properties of the peroxisome proliferator-activating receptorgamma (PPARgamma) into consideration, we established activation of PPARgamma in response to LPS/IFN-gamma by an electrophoretic mobility shift, supershift, and a reporter gene assay. The reporter contains a triple PPAR-responsive element (PPRE) in front of a thymidine kinase minimal promoter driving the luciferase gene. We demonstrated that PPRE decoy oligonucleotides, supplied in front of LPS/IFN-gamma, allowed a full oxidative burst to recover upon TPA addition. Furthermore, we suppressed the oxidative burst by using the PPARgamma agonists 15-deoxy-Delta12,14-prostaglandin J2, BRL 49653, or ciglitazone. No effect was observed with WY 14643, a PPARalpha agonist. We conclude that activation of PPARs, most likely PPARgamma, promotes macrophage desensitization, thus attenuating the oxidative burst. This process appears important during development of sepsis.

Attenuation of macrophage apoptosis by the cAMP-signaling system.

Previous studies revealed that expression and activation of cyclooxygenase-2 (Cox-2) conveyed a protective principle in murine macrophages, thus attenuating pro-apoptotic actions of chemotherapeutic agents or programmed cell death as a result of massive nitric oxide (NO) generation. Expression of Cox-2 was achieved by treatment of cells with lipopolysaccharide/interferon-gamma or nontoxic doses of NO releasing agents. We reasoned E-type prostanoid formation, and in turn an intracellular cAMP increase as the underlying protective mechanism. To prove our hypothesis, we analyzed the effects of lipophilic cAMP-analogs on NO, cisplatin, or etoposide induced apoptosis in RAW 264.7 macrophages. Selected apoptotic parameters comprised DNA fragmentation (diphenylamine assay), annexin V staining of phosphatidylserine, caspase activity (quantitated by the cleavage of a fluorogenic caspase-3-like substrate Ac-DEVD-AMC), and mitochondrial membrane depolarisation (delta psi). Western blots detected accumulation of the tumor suppressor protein p53, relocation of cytochrome c to the cytosol, and expression of the anti-apoptotic protein Bcl-xL. Prestimulation with lipophilic cAMP-analogs attenuated apoptosis with the notion that cell death parameters were basically absent. To verify gene induction by cAMP in association with protection we established activation of cAMP response element binding protein (CREB) by gel-shift analysis and moreover, treated macrophages with oligonucleotides containing a cAMP-responsive element (CRE) in order to scavenge CREB. Decoy oligonucleotides, but not control oligonucleotides, attenuated cAMP-evoked protection and reestablished pro-apoptotic parameters. We conclude that gene induction by cAMP protects macrophages towards apoptosis that occurs as a result of excessive NO formation or addition of chemotherapeutica. Attenuating programmed cell death by the cAMP-signaling system may be found in association with Cox-2 expression and tumor formation.

Modulation of nitric oxide-evoked apoptosis by the p53-downstream target p21(WAF1/CIP1).

When produced in excess, the inflammatory mediator nitric oxide (NO) attenuates cell-cycle progression at the G1 phase in tight correlation with p21(WAF1/CIP1) expression, provokes accumulation of the tumor suppressor p53, and initiates apoptosis/necrosis as judged on cell accumulation in the sub-G1 phase. To verify the role of p21(WAF1/CIP1) in modulating cell-cycle arrest vs. apoptosis, we transfected stably antisense p21(WAF1/CIP1)-encoding plasmids. Following NO exposure, accumulation of p21(WAF1/CIP1), but not p53, was largely attenuated in antisense p21(WAF1/CIP1) transfectants. Moreover, the G1 cell-cycle arrest was abrogated, and cells were sensitized toward apoptosis compared with parent macrophages. In contrast, antisense elimination of p53 attenuated p53 as well as p21(WAF1/CIP1) expression, abolished the G1 cell-cycle arrest, and prevented apoptosis. We conclude that p21(WAF1/CIP1) is a downstream target of p53 in macrophages that modulate the sensitivity toward the immune-modulator NO.

Superinduction of cyclooxygenase-2 by NO(*) and agonist challenge involves transcriptional regulation mediated by AP-1 activation.

Superinduction of cyclooxygenase-2, in murine RAW 264.7 macrophages as well as human pulmonary type II A549 epithelial cells, is achieved by the simultaneous addition of agonists such as lipopolysaccharide or interleukin-1beta and the NO(*) donor S-nitrosoglutathione. NO(*)-evoked superinduction of cyclooxygenase-2 in the presence of agonists was dose-dependent and required transcriptional as well as translational regulation. We sought to further analyze NO(*)-elicited superinduction at the level of the transcription factor NF-kappaB that is obligatory for cyclooxygenase-2 expression. NO(*)-mediated NF-kappaB activation was restricted to low concentrations of S-nitrosoglutathione (50-200 microM), while a higher dose of S-nitrosoglutathione (1 mM) was ineffective. Not observing a correlation between NF-kappaB activation and cyclooxygenase-2 expression under NO(*)-delivery stimulated our interest in analyzing AP-1. NO(*) efficiently activated AP-1 at all concentrations tested. The involvement of AP-1 in promoting cyclooxygenase-2 superinduction was established in cells transfected with the dominant-negative c-Jun mutant, TAM-67. Enhanced expression of cyclooxygenase-2 by lipopolysaccharide/S-nitrosoglutathione-treatment was attenuated in TAM-67 transfectants, while the response to lipopolysaccharide alone remained unaffected. We conclude that AP-1 activation exclusively conveys the NO(*) signal that is required for superinduction of cyclooxygenase-2. Superinduction of cyclooxygenase-2 is restricted to a situation where both, NF-kappaB and AP-1 are activated. Under inflammatory conditions this might be achieved by the costimulatory signals provided by agonist challenge and NO(*).

NO-Evoked macrophage apoptosis is attenuated by cAMP-induced gene expression.

BACKGROUND: Previous work has suggested that an increase in expression of cyclooxygenase-2, concomitant formation of E-type prostanoids, and in turn intracellular cAMP conveys macrophage resistance against apoptosis. MATERIALS AND METHODS: We analyzed the effects of lipophilic cAMP analogs on nitric oxide (NO)-induced apoptosis in RAW 264.7 macrophages and human primary monocyte-derived macrophages. Parameters comprised DNA fragmentation (diphenylamine assay), annexin V staining of phosphatidylserine, caspase activity (quantitated by the cleavage of a fluorogenic caspase-3-like substrate Ac-DEVD-AMC), and mitochondrial membrane depolarization (DeltaPsi), analyzed using DiOC(6)(3). Western blots detected accumulation of the tumor suppressor protein p53, relocation of cytochrome c, and expression of the antiapoptotic protein Bcl-X(L). A cAMP response-element decoy approach confirmed cAMP-dependent gene induction. RESULTS: We verified resistance of murine and human macrophages against NO donors such as S-nitrosoglutathione or spermine-NO by pre-exposing cells to lipophilic cAMP analogs or by pretreatment with lipopolysaccaride, interferon-gamma, and N(G)-nitroarginine-methylester for 15 hr. Cellular prestimulation decreased NO-evoked apoptosis, as apoptotic parameters were basically absent. Macrophage protection was not achieved during a short period of preexposure, i.e., 1 hr. To verify gene induction as the underlying protective principle, we treated RAW cells with oligonucleotides containing a cAMP-responsive element in order to scavenge cAMP response element-binding protein prior to its promoter-activating ability. Decoy oligonucleotides, but not an unrelated control oligonucleotide, weakened cAMP-evoked protection and re-established a p53 response following NO addition. CONCLUSION: Gene induction by cAMP protects macrophages against apoptosis that occurs as a result of excessive NO formation. Decreasing programmed cell death of macrophages may perpetuate inflammatory conditions in humans when macrophages become activated in close association with innate immune responses.

Nitric oxide (NO): an effector of apoptosis.

It is appreciated that the production of nitric oxide (NO) from L-arginine metabolism is an essential determinate of the innate immune system, important for nonspecific host defense, as well as tumor and pathogen killing. Cytotoxicity as a result of a substantial NO-formation is established to initiate apoptosis, characterized by upregulation of the tumor suppressor p53, changes in the expression of pro- and anti-apoptotic Bcl-2 family members, cytochrome c relocation, activation of caspases, chromatin condensation, and DNA fragmentation. Proof for the involvement of NO was demonstrated by blocking adverse effects by NO-synthase inhibition. However, NO-toxicity is not a constant value and NO may achieve cell protection as well. In part this is understood by transcription and translation of protective proteins, such as cyclooxygenase-2. Alternatively, protection may result as a consequence of a diffusion controlled NO/O2- (superoxide) interaction that redirects the apoptotic initiating activity of NO towards protection. NO is endowed with the unique ability to initiate and to block apoptosis, depending on multiple variables that exist to be elucidated. The crosstalk between cell destructive and protective signaling pathways under the modulatory influence of NO will determine the impact of NO in apoptotic cell death and survival.

Superoxide attenuates macrophage apoptosis by NF-kappa B and AP-1 activation that promotes cyclooxygenase-2 expression.

Macrophages are a major source of cytokines and proinflammatory radicals such as superoxide. These mediators can be both produced and utilized by macrophages in autocrine-regulatory pathways. Therefore, we studied the potential role of oxygen radical-regulatory mechanisms in reprogramming macrophage apoptosis. Preactivation of RAW 264.7 cells with a nontoxic dose of the redox cycler 2,3-dimethoxy-1,4-naphthoquinone (5 microM) for 15 h attenuated S-nitrosoglutathione (1 mM)-initiated apoptotic cell death and averted accumulation of the tumor suppressor p53, which is indicative for macrophage apoptosis. Preactivation with superoxide promoted cyclooxygenase-2 induction that was NF-kappa B and AP-1 mediated. NF-kappa B activation was confirmed by p50/p65-heterodimer formation, I kappa B-alpha degradation, and stimulation of a NF-kappa B luciferase reporter construct. Furthermore, a NF-kappa B decoy approach abrogated cyclooxygenase-2 (Cox-2) expression as well as inducible protection. The importance of AP-1 for superoxide-mediated Cox-2 expression and cell protection was substantiated by using the extracellular signal-regulated kinase-inhibitor PD98059 and the p38-inhibitor SB203580, which blocked Cox-2 expression. In corroboration, Cox-2 expression was hindered by a dominant-negative c-jun mutant (TAM67). Protection from apoptosis was verified in human macrophages with the notion that superoxide promoted Cox-2 expression, which in turn attenuated nitric oxide-evoked caspase activation. We conclude that the sublethal generation of oxygen radicals reprograms macrophages by NF-kappa B and AP-1 activation. The resulting hyporesponsiveness reveals an attenuated apoptotic program in association with Cox-2 expression.

Activation of the cell death program by nitric oxide involves inhibition of the proteasome.

The ubiquitin/proteasome pathway mediates the degradation of many short-lived proteins that are critically involved in the regulation of cell proliferation and cell death, including the tumor suppressor protein p53. Accumulation of p53 and induction of apoptosis in RAW 264.7 macrophages in response to nitric oxide are well established. However, the molecular mechanisms involved in nitric oxide-induced p53 accumulation are unknown. Here we show that, similar to nitric oxide, treatment of macrophages with specific proteasome inhibitors, including clastolactacystin-beta-lactone, induces p53 accumulation and apoptosis, suggesting that nitric oxide may affect the activity of the proteasome. In support of this hypothesis, both exposure of cells to S-nitrosoglutathione and stimulation of endogenous nitric oxide production by lipopolysaccharide/interferon-gamma treatment result in inhibition of proteasome activity as measured in vitro by the degradation of the proteasome-specific substrate succinyl-Leu-Leu-Val-Tyr-4-methylcoumarin-7-amide. Moreover, chemically diverse nitric oxide donors interfere with proteasome-mediated degradation of polyubiquitinated p53 in vitro. These data imply that nitric oxide-induced apoptosis and accumulation of p53 are, at least in part, mediated by inhibition of the proteasome.

NF-kappaB and AP-1 activation by nitric oxide attenuated apoptotic cell death in RAW 264.7 macrophages.

A toxic dose of the nitric oxide (NO) donor S-nitrosoglutathione (GSNO; 1 mM) promoted apoptotic cell death of RAW 264.7 macrophages, which was attenuated by cellular preactivation with a nontoxic dose of GSNO (200 microM) or with lipopolysaccharide, interferon-gamma, and NG-monomethyl-L-arginine (LPS/IFN-gamma/NMMA) for 15 h. Protection from apoptosis was achieved by expression of cyclooxygenase-2 (Cox-2). Here we investigated the underlying mechanisms leading to Cox-2 expression. LPS/IFN-gamma/NMMA prestimulation activated nuclear factor (NF)-kappaB and promoted Cox-2 expression. Cox-2 induction by low-dose GSNO demanded activation of both NF-kappaB and activator protein-1 (AP-1). NF-kappaB supershift analysis implied an active p50/p65 heterodimer, and a luciferase reporter construct, containing four copies of the NF-kappaB site derived from the murine Cox-2 promoter, confirmed NF-kappaB activation after NO addition. An NF-kappaB decoy approach abrogated not only Cox-2 expression after low-dose NO or after LPS/IFN-gamma/NMMA but also inducible protection. The importance of AP-1 for Cox-2 expression and cell protection by low-level NO was substantiated by using the extracellular signal-regulated kinase inhibitor PD98059, blocking NO-elicited Cox-2 expression, but leaving the cytokine signal unaltered. Transient transfection of a dominant-negative c-Jun mutant further attenuated Cox-2 expression by low-level NO. Whereas cytokine-mediated Cox-2 induction relies on NF-kappaB activation, a low-level NO-elicited Cox-2 response required activation of both NF-kappaB and AP-1.

The AT-rich region between -54 to -66 is important for the promoter activity of interleukin-10 in Epstein-Barr virus positive Burkitt's lymphoma cells.

IL-10 is an important regulatory cytokine. The recent characterization of the 5'-flanking region of IL-10 led to the identification of the promoter region. The infection of B cells with EBV induces IL-10 production which may contribute to EBV-induced transformation. In the present report, IL-10 promoter elements involved in the constitutive expression of IL-10 in EBV-positive lymphoma cells are described. The AT-rich region between -54/-66 from the transcriptional start site was found to be important for IL-10-promoter activity in BL36. A point mutation at position -60 (T/A) was associated with over 90% reduction of luciferase activity in the cell lines BL36 and BL74. The conversion of A/T at position -57 led to enhanced promoter activity. In addition the AT-rich region could serve as an enhancer for the beta-globin basic promoter. In BJAB cells (EBV-negative), sequences between -205/-139 rather than the AT-rich region were involved in IL-10 promoter regulation. This underlines the importance of the AT-rich region for EBV-associated IL-10 promoter regulation. Our results further the understanding of how the IL-10 gene could be regulated in B cell lymphomas.

Etoposide and cisplatin induced apoptosis in activated RAW 264.7 macrophages is attenuated by cAMP-induced gene expression.

Previous observations suggest expression of cyclooxygenase-2 to convey macrophage protection towards apoptotic cell death. We reasoned prostaglandin formation and in turn a cAMP increase as the underlying protective principle. Here we report that exposure of macrophages to lipopolysaccharide/interferon-gamma or lipophilic cAMP analogs such as dibutyryl-cAMP or 8-bromo-cAMP for 15 h attenuated DNA fragmentation and accumulation of the tumor suppressor p53 in response to the chemotherapeutic agents cisplatin and etoposide, compared to cells that received chemotherapeutic agents only. In contrast, a 1 h lasting preexposure period revealed no protection. The demand for a long incubation period with cAMP-derivates implied cAMP-mediated gene activation as the underlying principle. Therefore, we treated cells with oligonucleotides containing a cAMP-response element (CRE) binding site. Using this decoy-approach we scavaged activated cAMP response element binding protein prior to its promoter activating ability. Incubating macrophages with decoy, but not with control oligonucleotides, reduced cAMP evoked protection and simultaneously restored p53 accumulation in response to chemotherapeutic agents. Our studies demonstrate that cAMP-initiated gene activation regulates the sensitivity towards DNA damaging agents via inhibition of a p53 dependent pathway.

Nitric oxide and its role in apoptosis.

Nitric oxide (NO.), a potentially toxic molecule, has been implicated in a wide range of diverse (patho)physiological processes. It is appreciated that the production of NO. from L-arginine is important for nonspecific host defense, helping to kill tumors and intracellular pathogens. Cytotoxicity as a result of a massive NO.-formation is now established to initiate apoptosis. Apoptotic cell death in RAW 264.7 macrophages and several other systems as a result of inducible NO-synthase activation comprises upregulation of the tumor suppressor p53, activation of caspases, chromatin condensation, and DNA fragmentation. The involvement of NO was established by blocking adverse effects by NO-synthase inhibition. Overexpression of the antiapoptotic protein Bcl-2 rescued cells from apoptosis by blocking signal propagation downstream of p53 and upstream of caspase activation. As the wide variety of NO.-effects is achieved through its interactions with targets via redox and additive chemistry, the biological milieu, as a result of internal and external stimuli, may modulate toxicity. Therefore, transducing pathways of NO. are not only adopted to cytotoxicity but also refer to cell protection. NO.-signaling during protection from apoptosis is in part understood by the requirement of gene transcription and protein synthesis. NO.-formation causes upregulation of protective proteins such as heat shock proteins, cyclooxygenase-2, or heme oxygenase-1 which in a cell specific way may attenuate apoptotic cell death. Alternatively, protection may result as a consequence of a diffusion controlled NO./O2- (superoxide) interaction. The NO./O2--interaction redirects the apoptotic initiating activity of either NO. or O2- towards protection as long as reduced glutathione compensates the resultant oxidative stress. Protective principles may further arise from cyclic GMP formation or thiol modification. NO shares with other toxic molecules such as tumor necrosis factor-alpha the unique ability to initiate and to block apoptosis, depending on multiple variables that are being elucidated. The crosstalk between cell destructive and protective signaling pathways, their activation or inhibition under the modulatory influence of NO. will determine the role of NO in apoptotic cell death.

Apoptotic cell death and nitric oxide: activating and antagonistic transducing pathways.

Nitric oxide (NO) is a unique diffusible molecular messenger that occupies central roles in mammalian pathophysiology. Overproduction of NO is important for nonspecific "host" defense, helping to kill tumors and intracellular pathogens. Cytotoxicity as a result of long-lasting NO generation is now established to initiate apoptosis. Apoptotic cell death defines morphological alterations and distinctive biochemical events that lead to cell demise. NO-mediated apoptosis comprises upregulation of the tumor suppressor protein p53, activation of proteases known as caspases, chromatin condensation, DNA laddering, and is associated with alterations in the expression of apoptotic associated proteins that belong to the Bc1-2 family. An active role of NO was established by blocking adverse effects by NO-synthase inhibitors. Overexpression of the classical antiapoptotic protein Bc1-2 rescued cells from apoptosis by attenuating signaling downstream of p53 and upstream of caspase activation. Accumulating evidence suggests that transducing mechanisms can intersect and therefore a cell response to a given stimulus may alter significantly. As a result, transducing pathways of NO are not only adapted to cytotoxicity but also refer to cell protection. Protection from NO-elicited apoptosis may result as a consequence of a diffusion controlled NO/O2- (superoxide) interaction. The NO/O2- interaction redirects the apoptotic initiating activity of radicals (NO or O2-) towards protection as long as reduced glutathione compensates the resultant oxidative stress. Further, NO-mediated protective principles are understood on the basis of gene transcription of protective proteins such as heat shock proteins, hemeoxygenase-1, or cyclooxygenase-2 that attenuate cell injury in a cell specific way. The crosstalk between destructive and protective principles as a result of NO formation will determine the role of NO in cell injury. The balance between pro- and anti-apoptotic signaling mechanisms, their activation or deactivation as a result of NO formation, will allow cells to cope with NO or to exit into apoptosis.

Cyclooxygenase-2: an essential regulator of NO-mediated apoptosis.

Lipopolysaccharide/interferon gamma up-regulated inducible nitric oxide synthase and caused nitric oxide generation and concomitant apoptotic cell death in RAW 264.7 macrophages. Exogenously supplied nitric oxide donors such as S-nitrosoglutathione produced equivalent alterations. Preactivation of macrophages with a combination of lipopolysaccharide/interferon gamma under conditions of blocked NO synthase--N(G)-monomethyl-L-arginine addition--or stimulation with a low, nondestructive dose of S-nitrosoglutathione conferred protection against high and thus apoptotic NO concentrations. Here we report that induction of cyclooxygenase-2 during the preactivation period is a critical regulator of macrophage apoptosis. Under resting conditions, macrophages do not express cyclooxygenase-2, whereas lipopolysaccharide/interferon gamma/N(G)-monomethyl-L-arginine prestimulation for 12-15 h caused protein expression. In parallel, preactivation of RAW cells with a low, nontoxic dose of S-nitrosoglutathione promoted protection and cyclooxygenase-2 up-regulation. To prove cyclooxygenase-2 involvement during protection, we stably transfected RAW 264.7 macrophages with a rat cyclooxygenase-2 expression vector. Cyclooxygenase-2 overexpressing macrophages, preactivated with the calcium liberating and thus phopholipase A2-activating agent A23187, revealed protection against exogenously supplied NO. Protection afforded by lipopolysaccharide/interferon gamma/N(G)-monomethyl-L-arginine prestimulation was completely reversed by the addition of the cyclooxygenase-2 selective inhibitor NS-398 or in macrophages stably transfected with an antisense cyclooxygenase-2 expression vector. Our results point to cyclooxygenase-2 induction by lipopolysaccharide/interferon gamma/N(G)-monomethyl-L-arginine or low-dose nitric oxide pretreatment conferring macrophage protection to the apoptotic action of nitric oxide.

Expression of p56lck in B-cell neoplasias.

The protooncogene p56lck is considered to participate in malignant transformation of lymphoid cells. In order to evaluate the role of this tyrosine kinase in B cell neoplasias, we investigated the expression of p56lck by Western blot analysis. In 12/16 Burkitt's lymphoma derived cell lines, 3/3 lymphoblastoid cell lines, 1/6 Hodgkin's disease derived cell lines, and 10/10 freshly isolated chronic lymphocytic leukemia cells constitutive expression of the protein was detected. Protein tyrosine kinase assays detected a catalytic active form of p56lck in all p56lck expressing samples. Stimulation experiments of the different cell lines and primary tumour cells by the phorbol ester TPA and the B-cell specific stimulation with SAC/anti-IgM respectively indicated a change of the expression level in comparison with the unstimulated cells and, a higher molecular weight species of the protein tyrosine kinase p56lck was observed. This was probably due to hyperphosphorylation of p56lck. No correlation between an infection with the Epstein-Barr virus and the expression of p56lck was found in the cell lines used and in primary tumour cells. Inhibition of p56lck activity by the specific inhibitor 4-amino-6-hydroxyflavone revealed a decrease of proliferation of the T-cell line Jurkat, but not of the Burkitt's lymphoma cell lines. In the analysed cell lines we found a reduction of the kinase activity of p56lck of approximately 70%. These results suggest that lck may contribute to the maintenance of the transformation of the analysed B cell neoplasias but that lck does not support a model for an initial event in B cell transformation.

Cytokine and low-level nitric oxide prestimulation block p53 accumulation and apoptosis of RAW 264.7 macrophages.

Nitric oxide causes apoptotic cell death in RAW 264.7 macrophages. The cellular response to the NO donor S-nitrosoglutathione (GSNO) comprises an apoptotic morphology and DNA fragmentation, which largely depends on the accumulation of the tumor suppressor gene product p53. Pre-treatment of macrophages with LPS, IFN-gamma in the presence of NG-monomethyl-L-arginine (NMMA) imparts resistance to apoptotic cell death, normally elicited by exogenously-supplied GSNO. Similarly, pre-treatment with low-dose GSNO (25-200 microM) conferred resistance from a second exposure to a higher dose of GSNO (1 mM). Protection is comprehended at the level of blocked p53 accumulation. Upregulation of protective mechanisms in response to non-lethal NO concentrations or by LPS, cytokine pre-stimulation may redirect the ability of nitric oxide to upregulate p53 and to initiate macrophage apoptosis, thereby modulating cellular susceptibility towards NO-intoxication.

Isolation of the human interleukin 10 promoter. Characterization of the promoter activity in Burkitt's lymphoma cell lines.

Interleukin 10 (IL-10) is a pleiotropic growth and differentiation factor with potent suppressor functions on macrophages, T cells and NK cells and contributes to the regulation of proliferation and differentiation of B cells. The expression of IL-10 appears to be tightly regulated, as the levels of constitutive expression in normal cells is extremely low. In contrast to normal haematopoetic cells, Epstein-Barr virus (EBV)-immortalized B cells and EBV-positive Burkitt's lymphoma cells express high levels of IL-10 constitutively. In this report we have cloned and sequenced IL-10 promoter fragments and analysed their activity in EBV-positive Burkitt's lymphoma cells. A nested set of DNA fragments from the IL-10 gene 5'-flanking region was placed upstream of the luciferase gene and assayed for their ability to direct luciferase expression in Burkitt's lymphoma cells. We have identified elements within the 5'-flanking region of the human IL-10 gene which can activate or suppress the constitutive expression of IL-10. The essential promoter of the IL-10 gene, which induces low levels of luciferase expression, was found to require the major start site of transcription (+1), a TATA-box (-77) and up to 150 additional 5' nucleotides. Positive regulatory sequences are located between -1100/-900. Negative regulatory elements which abolish luciferase activity were identified between -800/-300.