Apoptosis in chronic obstructive pulmonary disease]

Apoptosis is a critical mechanism controlling cellularity in various tissues. It is so far unknown whether apoptosis plays a critical role in the pathogenesis and development of chronic obstructive pulmonary disease (COPD). However, recent evidence suggests that apoptosis may occur in vascular endothelial cells and/or alveolar epithelial cells in COPD lungs, thereby potentially contributing to lung tissue destruction seen in COPD. Apoptosis may also influence cellular infiltrates into the lung, another pathologic feature of COPD, because the survival of inflammatory cells such as neutrophils, lymphocytes, and macrophages are critically determined by the mechanism of apoptosis.     

Apoptosis: the complex scenario for a silent cell death.

In multicellular organisms, homeostasis is maintained by a balance between cell proliferation and apoptosis (programmed cell death). It is a physiological form of cell death responsible for the deletion of not reparable damaged, mutated, or cells which have lost their function. Apoptosis can be distinguished by morphological and biochemical characteristics from necrosis (pathological cell death). Apoptotic cell death does not disturb surrounding cells. To achieve the elimination of cells without an inflammatory reaction, a complex interplay of several molecules is necessary. Apoptosis either starts from the cell surface (CD95-CD95L), the mitochondrion or from the nucleus. The cell biological events run in a cascaded fashion and are regulated by either enhancer or anti-apoptotic signals that probably may stop the executions machinery. The knowledge about apoptosis helps to understand pathophysiologic conditions, to better diagnose and treat them by molecular radiological techniques.     

Characterization of two distinct mechanisms for induction of apoptosis in human vascular endothelial cells.

Tissue homeostasis is fundamentally influenced by the functional integrity and state of endothelial cells. Survival and death of endothelial cells are encountered in cardiovascular disease and may, moreover, affect and determine the development of atherosclerosis and restenosis following intracoronary therapeutical interventions. Apoptosis was studied in cultured human umbilical vein endothelial cells (HUVEC) to investigate the regulation of endothelial cell death following serum/growth factor depletion as well as incubation with actinomycin-D. Apoptosis was verified by DNA fragmentation and quantified by fluorescence activated cell sorting (FACS) analysis after TdT-mediated deoxyuridine-triphosphate nick end-labeling (TUNEL). An ELISA was used for detecting intracytoplasmatic nucleosomes. Untreated HUVEC showed 16+/-6% TUNEL positive cells after 24 hours as analyzed by FACS. Serum/growth factor depletion increased apoptosis by 79+/-7%, while 50 ng/ml of the pro-apoptotic drug actinomycin-D induced comparable effects (72+/-11%). Apoptosis by serum/ growth factor depletion could be blocked completely by the anti-apoptotic agent cycloheximide (2 microg/ml), but was ineffective in blocking actinomycin-D-induced apoptosis. Pyrrolidine dithiocarbamate (PDTC) also acted as an anti-apoptotic agent by blocking apoptosis induced by actinomycin-D, but had no effect on apoptosis induced by factor depletion. Thus, two independent mechanisms for regulation of apoptosis are suggested to be present in human vascular endothelial cells.     

Apoptosis in diseases of the liver

Apoptosis, or programmed cell death, and the elimination of apoptotic cells are crucial factors in the maintenance of liver health Apoptosis allows hepatocytes to die without provoking a potentially harmful inflammatory response In contrast to necrosis, apoptosis is tightly controlled and regulated via several mechanisms, including Fas/Fas ligand interactions, the effects of cytokines such as tumor necrosis factor alpha (TNF-alpha) and transforming growth factor beta (TGF-beta), and the influence of pro- and antiapoptotic mitochondria-associated proteins of the B-cell lymphoma-2 (Bcl-2) family. Efficient elimination of apoptotic cells in the liver relies on Kupffer cells and endothelial cells and is thought to be regulated by the expression of certain cell surface receptors. Liver disease is often associated with enhanced hepatocyte apoptosis, which is the case in viral and autoimmune hepatitis, cholestatic diseases, and metabolic disorders. Disruption of apoptosis is responsible for other diseases, for example, hepatocellular carcinoma. Use and abuse of certain drugs, especially alcohol, chemotherapeutic agents, and acetaminophen, have been associated with increased apoptosis and liver damage. Apoptosis also plays a role in transplantation-associated liver damage, both in ischemia/reperfusion injury and graft rejection. The role of apoptosis in various liver diseases and the mechanisms by which apoptosis occurs in the liver may provide insight into these diseases and suggest possible treatments.     

Apoptosis of human vascular smooth muscle cells derived from normal vessels and coronary atherosclerotic plaques.

We studied death of human vascular smooth muscle cells derived from coronary plaques and normal coronary arteries and aorta. Cells from normal arteries underwent death only upon removal of serum growth factors. In contrast, plaque-derived cells died even in high serum conditions, and death increased after serum withdrawal. Death was characteristically by apoptosis in both normal and plaque-derived cells, as determined by time-lapse videomicroscopy, electron microscopy, and DNA fragmentation patterns. IGF-1 and PDGF were identified as potent survival factors in serum, whereas EGF and basic fibroblast growth factor had little effect. Stable expression of bcl-2, a protooncogene that regulates apoptosis in other cell lines, protected smooth muscle cells from apoptosis, although there was no detectable difference in endogenous bcl-2 expression between cells from plaques or normal vessels. We conclude that apoptosis of human vascular smooth muscle cells is regulated by both specific gene products and local cytokines acting as survival factors. Apoptosis may therefore regulate cell mass in the normal arterial wall and the higher rates of apoptosis seen in plaque smooth muscle cells may ultimately contribute to plaque rupture and breakdown and thus to the clinical sequelae of atherosclerosis.     

Apoptosis induced by HIV-1 infection of the central nervous system.

Apoptosis plays a role in AIDS pathogenesis in the immune system, but its role in HIV-1-induced neurological disease is unknown. In this study, we examine apoptosis induced by HIV-1 infection of the central nervous system (CNS) in an in vitro model and in brain tissue from AIDS patients. HIV-1 infection of primary brain cultures induced apoptosis in neurons and astrocytes in vitro as determined by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) and propidium iodide staining and by electron microscopy. Apoptosis was not significantly induced until 1-2 wk after the time of peak virus production, suggesting induction by soluble factors rather than by direct viral infection. Apoptosis of neurons and astrocytes was also detected in brain tissue from 10/11 AIDS patients, including 5/5 patients with HIV-1 dementia and 4/5 nondemented patients. In addition, endothelial cell apoptosis was frequently detected in the brain of AIDS patients and was confirmed by electron microscopy. Most of the apoptotic cells were not localized adjacent to HIV-1-infected cells, providing further evidence for induction by soluble factors. In six non-AIDS control patients with normal brain, apoptotic cells were absent or limited to rare astrocytes. However, TUNEL-positive neurons and astrocytes were frequently detected in seven patients with Alzheimer's disease or abundant senile plaques. These studies suggest that apoptosis is a mechanism of CNS injury in AIDS which is likely to be induced by soluble factors. The apoptosis of endothelial cells in the CNS raises the possibility that some of these factors may be blood-derived.     

Unraveling distinct intracellular signals that promote survival and proliferation: study of erythropoietin, stem cell factor, and constitutive signaling in leukemic cells

This review summarizes selected recent studies of the intracellular signals that allow erythroid cells to survive and proliferate under the control of erythropoietin (EPO) and alteration in signals that contribute to EPO-independent survival and proliferation. The hypothesis explored is that the proliferation and survival signals are distinct and can be separately studied with the proper cell lines and growth factor stimulation. The anti- and pro-apoptotic proteins Bcl-XL and BAD are highly implicated in EPO-dependent survival of erythroid cells. Stat5 activity appears to be upstream of Bcl-XL expression such that pathologic, constitutive activation of Stat5 may be a common event in leukemic cells that become resistant to apoptosis by constitutive expression of Bcl-XL. Other signals apparently also control the expression of Bcl-XL, such as the expression of JunB which seem to be required to suppress Bcl-XL expression when EPO is withdrawn. Apoptosis may also be triggered by inactivation of Bcl-XL by BAD. Dephosphorylation of BAD as a result of withdrawal of survival factors converts prosurvival BAD to proapoptotic BAD. Phosphorylation of BAD at the serine 112 residue seems critical to promoting survival. Constitutive activation of a kinase that phosphorylates BAD serine 112 may, therefore, contribute to resistance to apoptosis in leukemic cells. We describe the resistance of erythroleukemic cells to apoptosis induced by EPO withdrawal apparently caused by constitutive BAD phosphorylation. The resistance to apoptosis in these cells is reversed by treatment with the PI3-kinase inhibitor, LY294002, suggesting that resistance to apoptosis in these cells likely results from constitutive P13-kinase that is an upstream activator of an S-112 BAD kinase. The MAP kinase cascade is apparently active in EPO-dependent and stem cell factor (SCF)-dependent proliferation but not survival. In addition, autocrine tumor necrosis factor-a! (TNF-alpha) may also be a proliferation factor not affecting survival. P13-kinase seems to be required for full EPO-dependent proliferation but is not required for EPO-dependent survival (but it can promote survival when activated).     

Plasminogen activation: a mediator of vascular smooth muscle cell apoptosis in atherosclerotic plaques

BACKGROUND: Apoptosis of vascular cells is considered to be a major determinant of atherosclerotic plaque vulnerability and potential rupture. Plasmin can be generated in atherosclerotic plaques and recent in vitro data suggest that plasminogen activation may trigger vascular smooth muscle cell (VSMC) apoptosis. AIM: To determine whether plasminogen activation may induce aortic VSMC apoptosis ex vivo and in vivo. METHODS AND RESULTS: Mice with single or combined deficiencies of apolipoprotein E (ApoE) and plasminogen activator inhibitor-1 (PAI-1) were used. Ex vivo incubation with plasminogen of isolated aortic tunica media from PAI-1-deficient mice induced plasminogen activation and VSMC apoptosis, which was inhibited by alpha2-antiplasmin. In vivo, levels of plasmin, active caspase 3 and VSMC apoptotic index were significantly higher in atherosclerotic aortas from mice with combined ApoE and PAI-1 deficiencies than in those from littermates with single ApoE deficiency. A parallel decrease in VSMC density was observed. CONCLUSIONS: These data strongly suggest that plasminogen activation may contribute to VSMC apoptosis in atherosclerotic plaques.     

Prevention of Vascular Apoptosis in Myocardial Infarction by Losartan

BACKGROUND: Previous studies have demonstrated the occurrence of apoptosis in cardiomyocytes in different types of cardiovascular diseases. This report provides the first evidence for the presence of vascular apoptosis in myocardial infarction induced in rats by occluding the coronary artery for 7 weeks. METHODS AND RESULTS: Apoptosis was characterized by DNA fragmentation, upregulation of caspase-3, downregulation of poly (ADP-ribose) polymerase (PARP), increased c-fos mRNA expression and caspase-3/PARP ratio in aortic vascular smooth muscle cells. The results show apoptotic changes in 10-25% of the aortic vascular cells after myocardial infarction; these alterations were prevented after treating the 3-week operated animals with an angiotensin II receptor antagonist, losartan (25 mg/kg/day; intraperitoneal) for 4 weeks. Cultured rat aortic smooth muscle cells exposed to 10 nmol/L angiotensin II for 48 hours also exhibited apoptotic changes, which were inhibited by 10 nmol/L losartan. CONCLUSIONS: These results suggest that vascular apoptosis occurs in myocardial infarction, and this may be due to an increase in the circulating levels of angiotensin II.     

Role of apoptosis in atherosclerosis and its therapeutic implications

Atherosclerotic plaques develop as a consequence of the accumulation of circulating lipid and the subsequent migration of inflammatory cells (macrophages and T-lymphocytes) and VSMCs (vascular smooth muscle cells). Advanced plaques consist of a lipid-rich core, separated from the lumen by a fibrous cap composed of VSMCs, collagen and extracellular matrix. Plaque enlargement ultimately narrows the lumen (stenosis) causing angina. However, recent studies have emphasized that acute coronary syndromes (unstable angina/myocardial infarction) are caused by lesion erosion/rupture with superimposed thrombus formation on often small non-stenotic plaques. Thus current therapies work predominantly on stabilization of plaques rather than plaque regression. Apoptosis (programmed cell death) is increasingly observed as plaques develop, although the exact mechanisms and consequences of apoptosis in the development and progression of atherosclerosis are still controversial. Increased endothelial cell apoptosis may initiate atherosclerosis, whereas apoptosis of VSMCs and macrophages localizes in 'vulnerable' lesions, i.e. those most likely to rupture, and at sites of rupture. This review will focus on the regulation of apoptosis of cells within the vasculature, concentrating on the relevance of apoptosis to plaque progression and clinical consequences of vascular cell apoptosis.     

Apoptosis of human intestinal epithelial cells after bacterial invasion.

Epithelial cells that line the human intestinal mucosa are the initial site of host invasion by bacterial pathogens. The studies herein define apoptosis as a new category of intestinal epithelial cell response to bacterial infection. Human colon epithelial cells are shown to undergo apoptosis following infection with invasive enteric pathogens, such as Salmonella or enteroinvasive Escherichia coli. In contrast to the rapid onset of apoptosis seen after bacterial infection of mouse monocyte-macrophage cell lines, the commitment of human intestinal epithelial cell lines to undergo apoptosis is delayed for at least 6 h after bacterial infection, requires bacterial entry and replication, and the ensuing phenotypic expression of apoptosis is delayed for 12-18 h after bacterial entry. TNF-alpha and nitric oxide, which are produced as components of the intestinal epithelial cell proinflammatory program in the early period after bacterial invasion, play an important role in the later induction and regulation of the epithelial cell apoptotic program. Apoptosis in response to bacterial infection may function to delete infected and damaged epithelial cells and restore epithelial cell growth regulation and epithelial integrity that are altered during the course of enteric infection. The delay in onset of epithelial cell apoptosis after bacterial infection may be important both to the host and the invading pathogen since it provides sufficient time for epithelial cells to generate signals important for the activation of mucosal inflammation and concurrently allows invading bacteria time to adapt to the intracellular environment before invading deeper mucosal layers.     

Effects of angiotensin II type 1 and type 2 receptor on apoptosis

Apoptosis, a morphological form of programmed cell death required for control of cell populations, participates in reduced tissue volume associated with ventricular scarring. Prevention of apoptosis of excessive, damaged, or nonfunctioning cardiac or of infiltrating inflammatory cells is usually beneficial for the resolution of cardiac fibrosis. Angiotensin(Ang) II, the most important peptide that mediates the effects of the renin-angiotensin system, may play an important role in hypertension, hypertrophy, and interstitial fibrosis. Furthermore, AngII induced apoptosis of human venous endothelial cells, myocyte, and vascular smooth muscular cells by caspase cascade activation, and the both blockade of AngII type(AT)1 and AT2 receptor prevents AngII induced apoptosis, whereas selective agonistic stimulation of the AT2 receptor alone induces apoptosis. When AT1 or AT2 receptors are stimulated in vivo, apoptosis is enhanced in myocytes, myofibroblasts, and media smooth muscular cells. In the case of AT1 receptor stimulation, this may occur in cardiac myocytes secondary to ventricular hypertrophy. On the other hand, AT2 receptor stimulation induced apoptosis myofibroblasts associated with reduced interstitial fibrosis. Caspase-3 participates in the pathways of apoptosis triggered by in vivo AT1 and AT2 receptor stimulations.     

Oxidized LDL activates fas-mediated endothelial cell apoptosis.

Oxidized low density lipoproteins (OxLDL) promote chronic inflammatory responses in the vasculature that give rise to atherosclerotic plaques. Fas ligand (FasL) is naturally expressed on the vascular endothelium where it can induce apoptosis in Fas-expressing immune cells as they enter the vessel wall. Although vascular endothelial cells are normally resistant to Fas-mediated cell death, OxLDL were shown to induce apoptosis in cultured endothelial cells and endothelium of arterial explants by a process that could be inhibited with Fas L neutralizing antibodies. OxLDL-induced cell death was also reduced in the aortic endothelium cultured from gld (FasL-/-) and lpr (Fas-/-) mice as compared with wild-type mice. OxLDL acted by sensitizing endothelial cells to death signals from the Fas receptor. Thus, the ability of OxLDL to promote Fas-mediated endothelial cell suicide may be a feature that contributes to their atherogenicity.     

Apoptosis signal-regulating kinase 1-mediated signaling pathway regulates hydrogen peroxide-induced apoptosis in human pulmonary vascular endothelial cells

OBJECTIVE: Reactive oxygen species initiate pulmonary vascular endothelial cell damage leading to an increase in endothelial permeability resulting in the production of pulmonary edema. Apoptosis signal-regulating kinase (ASK)-1 is a ubiquitously expressed mitogen-activated protein kinase kinase kinase (MAPKKK) that activates the MKK3/MKK6-p38 MAPK and the SEK1-c-Jun N-terminal kinase (JNK) signaling cascade. ASK1 has been implicated in cytokine- and stress-induced apoptosis. However, little is known about the role of ASK1 in apoptosis in hydrogen peroxide (H2O2)-stimulated pulmonary vascular endothelial cells and how ASK1-mediated apoptosis is executed. To clarify this issue, we examined the role of ASK1-p38 MAPK/JNK cascade in apoptosis and caspase-3 activation in H2O2-stimulated pulmonary vascular endothelial cells. DESIGN: Experimental laboratory study. SETTING: University laboratory. SUBJECTS: Normal human pulmonary artery endothelial cells. INTERVENTIONS: Western blot analysis and quantification of apoptosis in cells. MEASUREMENTS AND MAIN RESULTS: The results showed that H2O2 induced ASK1 phosphorylation and concomitantly p38 MAPK and JNK phosphorylation as well as induced caspase-3 activation in pulmonary vascular endothelial cells. To further characterize the role of ASK1 cascade in H2O2-induced apoptosis of pulmonary vascular endothelial cells, the dominant negative form of ASK1-stably transfected porcine artery endothelial cells was used. p38 MAPK and JNK phosphorylation, caspase-3 activation, and apoptosis in the dominant negative form of ASK1-stably transfected porcine artery endothelial cells were depressed compared with those in the parental porcine artery endothelial cells. CONCLUSION: ASK1-p38 MAPK/JNK cascade regulates apoptosis of H2O2-stimulated human pulmonary vascular endothelial cells.     

Rapid onset of intestinal epithelial and lymphocyte apoptotic cell death in patients with trauma and shock

OBJECTIVE: Apoptosis is a cellular suicide program that can be activated by cell injury or stress. Although a number of laboratory studies have shown that ischemia/reperfusion injury can induce apoptosis, few clinical studies have been performed. The purpose of this study was to determine whether apoptosis is a major mechanism of cell death in intestinal epithelial cells and lymphocytes in patients who sustained trauma, shock, and ischemia/ reperfusion injury. DESIGN: Intestinal tissues were obtained intraoperatively from 10 patients with acute traumatic injuries as a result of motor vehicle collisions or gun shot wounds. A control population consisted of six patients who underwent elective bowel resections. Apoptosis was evaluated by conventional light microscopy, laser scanning confocal microscopy using the nuclear staining dye Hoechst 33342, immunohistochemical staining for active caspase-3, and immunohistochemical staining for cytokeratin 18. SETTING: Academic medical center. PATIENTS: Patients with trauma or elective bowel resections. MEASUREMENTS AND MAIN RESULTS: Extensive focal crypt epithelial and lymphocyte apoptosis were demonstrated by multiple methods of examination in the majority of trauma patients. Trauma patients having the highest injury severity score tended to have the most severe apoptosis. Repeat intestinal samples obtained from two of the trauma patients who had a high degree of apoptosis on initial evaluation were negative for apoptosis at the time of the second operation. Tissue lymphocyte apoptosis was associated with a markedly decreased circulating lymphocyte count in 9 of 10 trauma patients. CONCLUSIONS: Focal apoptosis of intestinal epithelial and lymphoid tissues occurs extremely rapidly after injury. Apoptotic loss of intestinal epithelial cells may compromise bowel wall integrity and be a mechanism for bacterial or endotoxin translocation into the systemic circulation. Apoptosis of lymphocytes may impair immunologic defenses and predispose to infection.     

Glioma apoptosis induced by macrophages involves both death receptor-dependent and independent pathways

Apoptosis of glioma may represent a promising intervention for tumor treatment. Macrophages are able to induce apoptosis in a number of tumor cells, including glioma. It is known that apoptosis of cells is executed on either a death receptor-dependent or independent pathway. Whether and how apoptosis of glioma cells induced by activated macrophages is involved in these two pathways simultaneously are not known. Using in vitro and in vivo experimental models, we investigated Bcl-2 system and Fas/FasL channel, representing the death receptor-dependent and independent pathways, respectively, in glioma cells treated with the supernatant from the activated macrophages, which was rich in tumor necrosis factor-alpha and interferon-gamma. We found that levels of Fas and FasL were up-regulated both in vitro and in vivo, accompanying an increase in the expression of caspase-8. The number of apoptotic cells was also increased significantly, although the percentage of death cells exceeded the number of tumor cells positive for Fas or FasL. It was also evident that the expression of Bax was increased, whereas the level of Bcl-2 was decreased, in glioma cells treated with the supernatant from the activated macrophages. The alteration of molecules related to both death pathways led to apoptosis of glioma and the inhibition of xenograft glioma growth in mice. Apoptosis of glioma induced by the activated macrophage is executed by way of both death receptor-dependent and independent pathways, and such an apoptosis-induced approach can effectively inhibit the growth of glioma in vivo.     

Dysregulation of the genes controlling apoptosis in cancer development

Apoptosis is a cellular self-destruction mechanism involved in a variety of biological events. Cancer is a disorder of autonomous cell proliferation and accumulation, which is associated with the failure to undergo apoptosis in response to appropriate stimuli. Inhibition of apoptosis may be a prerequisite or acquired biological feature of various cancer cells. Resistance to apoptosis is achieved either by an increase in apoptosis resistance or decrease in apoptosis sensitivity. Some of the hereditary cancer syndrome patients have mutations in the genes to induce apoptosis, eventually leading to inhibition of apoptosis and cancer development.     

骨髓增生异常综合征富集造血祖细胞半胱天冬酶活性检测及意义

目的　了解骨髓增生异常综合征 (MDS)患者不同阶段骨髓造血祖细胞凋亡的变化及半胱天冬酶caspase3、caspase9的作用。方法　应用负筛选法纯化MDS患者骨髓造血祖细胞 (包括CD3 4 +和CD3 4 -细胞 ) ,通过AnnexinⅤ方法检测其凋亡 ,同时应用分光光度法测定细胞内caspase3、caspase9的活性。结果　①MDS RA组 12例 ,凋亡率为 39.5 % ;RAEB组 10例 ,凋亡率为 31.0 % ,两组凋亡率均明显高于对照组 (P <0 .0 1)。RAEB t/AML组 12例 ,凋亡率为 18.8% ,与对照组相比 ,差异无显著性。②MDS RA组caspase3活性较正常对照升高约 4 5倍 (P <0 .0 1) ,caspase9的活性较正常对照升高约 2 0倍(P <0 .0 1)。RAEB组 ,caspase3活性较正常对照升高约 14倍 (P <0 .0 1) ,caspase9的活性较正常对照升高 2倍余 (P <0 .0 1)。RAEB t/AML组 ,caspase3活性稍高于正常对照 (无统计学意义 ) ,caspase9的活性与正常对照相比 ,差异无显著性。③RAEB组中有 3例最终转为急性髓系白血病 (AML) ,其凋亡率、caspase3和caspase9的平均吸光度值均相应下降。结论　MDS患者骨髓造血祖细胞在疾病不同阶段凋亡率是不同的 ,caspase3、caspase9活性升高 ,可能是造成MDS骨髓造血祖细胞过度凋亡的重要原因 ,caspase9活性下降可能是MDS发展过程中骨髓造     

Activation-induced apoptosis in human macrophages: developmental regulation of a novel cell death pathway by macrophage colony- stimulating factor and interferon gamma

Activated macrophages (M phi s) are important participants in host defense, but their uncontrolled activation leads rapidly to septic shock and death. One mechanism for regulating other dangerous cells in the immune system is programmed cell death, or apoptosis. Monocytes are known to undergo spontaneous apoptosis upon leaving the circulation unless provided with specific survival signals, but mature tissue M phi s are more robust cells, and it was not clear that they could be similarly regulated by apoptosis. We now show that during differentiation monocytes rapidly lose their sensitivity to apoptosis triggered by passive cytokine withdrawal, but they may retain a novel pathway which initiates apoptosis after activation with specific stimuli (zymosan and phorbol esters). Sensitivity to activation-induced apoptosis was developmentally determined, being downregulated by the maturation-promoting cytokine macrophage colony-stimulating factor but stably upregulated by even transient exposure to the proinflammatory cytokine interferon gamma (IFN-gamma). Apoptosis began within 2-4 h of activation, occurred in > 95% of susceptible cells, and in mixed cocultures selectively affected only those M phi s with a history of IFN-gamma priming. Consistent with a possible role for protein kinase C in the signaling pathway leading to cell death, the kinase inhibitor staurosporine was protective against both phorbol ester- and zymosan- induced apoptosis. Our studies describe a novel form of activation- induced M phi apoptosis which is developmentally regulated by two physiologically relevant cytokines. We speculate that apoptosis may serve to restrict the destructive potential of inflammatory M phi s.     

Induced apoptosis supports spread of adenovirus vectors in tumors.

Selectively replicating viruses hold promise as anticancer agents. To eliminate the tumor, these viruses must efficiently spread throughout the tumor and induce oncolysis. We hypothesized that viral release and spread could be supported by apoptosis induced after assembly of de novo-produced virions in tumor cells. As a model to test this, we employed an adenovirus vector that replicated in human tumor cell lines. Expression of a dominant-negative I-kappaB from this vector sensitized tumor cells to recombinant human tumor necrosis factor alpha (TNF-alpha)-mediated apoptosis. We found that apoptosis induced during viral DNA replication compromised virus production, whereas apoptosis induced after virion assembly enhanced viral release from infected cells and dissemination. Electron microscopy demonstrated that viral particles were associated with or included in apoptotic bodies whose phagocytosis by neighboring cells provides a potential means for viral spread. Apoptosis induced after viral replication also supported spread in vivo, in subcutaneous tumors or liver metastases, resulting in a delay of tumor growth. Our findings could be applicable to other selectively replicating viruses or antitumor strategies that involve application of proapoptotic or cytolytic agents.