Bacterial programmed cell death of cerebral endothelial cells involves dual death pathways

Major barriers separating the blood from tissue compartments in the body are composed of endothelial cells. Interaction of bacteria with such barriers defines the course of invasive infections, and meningitis has served as a model system to study endothelial cell injury. Here we report the impressive ability of Streptococcus pneumoniae, clinically one of the most important pathogens, to induce 2 morphologically distinct forms of programmed cell death (PCD) in brain-derived endothelial cells. Pneumococci and the major cytotoxins H2O2 and pneumolysin induce apoptosis-like PCD independent of TLR2 and TLR4. On the other hand, pneumococcal cell wall, a major proinflammatory component, causes caspase-driven classical apoptosis that is mediated through TLR2. These findings broaden the scope of bacterial-induced PCD, link these effects to innate immune TLRs, and provide insight into the acute and persistent phases of damage during meningitis.     

Staurosporine induces apoptosis of melanoma by both caspase-dependent and -independent apoptotic pathways

Staurosporine has long been used in vitro as an initiator of apoptosis in many different cell types, but the mechanism involved remains poorly understood. In the present study, we have examined the apoptosis-inducing potential of staurosporine in cultured melanoma cell lines and dissected the staurosporine-induced apoptotic signaling pathway. We report that although staurosporine activated Bax and the mitochondrial caspase-dependent apoptotic pathway, it also induced apoptosis of melanoma by caspase-independent pathways. The caspase-dependent apoptotic pathway was activated relatively soon after exposure to staurosporine and was associated with release of cytochrome c and Smac/DIABLO from mitochondria and cleavage of poly(ADP-ribose) polymerase and inhibitor of caspase-activated DNase. This pathway was inhibitable by broad caspase inhibitors. A second apoptotic pathway that appeared to be involved in late apoptotic events was caspase independent in that inhibitors of caspases did not prevent the late onset of apoptosis. Overexpression of Bcl-2 inhibited the early onset of apoptosis but not the later, caspase-independent pathway. Apoptosis-inducing factor may be responsible for the late apoptotic execution in that its translocation from mitochondria into the nucleus coincided with the late onset of apoptosis and could not be inhibited by either a pan-caspase inhibitor or overexpression of Bcl-2. Our results indicate that staurosporine is able to bypass resistance of melanoma cells to mitochondrial caspase-dependent apoptotic pathways; hence, derivatives of staurosporine may warrant further evaluation either alone or with other apoptosis-inducing agents.     

Mode of action and molecular target of ECH, a specific inhibitor of death receptor-dependent apoptosis

ECH (epoxycyclohexenone) specifically blocks death receptor-mediated apoptosis induced by anti-Fas antibody, Fas ligand, or TNF-alpha, whereas it has no effect on death receptor independent apoptosis induced by staurosporine, MG-132, C2-ceramide, or UV irradiation. ECH blocks the activation of pro-caspase-8 in the death-inducing signaling complex (DISC), even though recruitment of FADD and pro-caspase-8 is not affected. In Fas ligand treated cells, ECH is only able to inhibit the activation of pro-caspase-8 and it has no effect on the already-activated caspase-8. ECH has a relatively higher affinity to pro-caspase-8, although it directly binds both pro- and active-form of caspase-8. In conclusion, ECH targets pro-caspase-8 and blocks the self-activation of pro-caspase-8 in the DISC, and thus selectively inhibits death receptor-mediated apoptosis. Moreover novel non-peptide inhibitors, RKTS-33 & RKTS-34 that are chemically synthesized derivatives of ECH have been developed.     

Interleukin 1 is released by murine macrophages during apoptosis induced by Shigella flexneri.

Peritoneal macrophages undergoing apoptosis induced by Shigella flexneri infection release the inflammatory cytokine interleukin 1 (IL-1), but not IL-6 or tumor necrosis factor alpha (TNF alpha). Wild type shigella causes a very fast and significant release of IL-1 from prestimulated peritoneal macrophages, before the cell's integrity is compromised. Both IL-1 alpha and IL-1 beta are released, IL-1 beta in its mature processed form. IL-1 is released from presynthesized cytoplasmic pools. These results demonstrate that bacteria-induced apoptosis of macrophages may play an active role in vivo by releasing IL-1, which in turn mediates an early inflammatory response in epithelial tissues.     

Caspase-mediated apoptosis and caspase-independent cell death induced by irofulven in prostate cancer cells

Irofulven (hydroxymethylacylfulvene) is a novel antitumor drug, which acts by alkylating cellular macromolecular targets. The drug is a potent inducer of apoptosis in various types of tumor cells, whereas it is nonapoptotic in normal cells. This study defined molecular responses to irofulven involving mitochondrial dysfunction and leading to death of prostate tumor LNCaP-Pro5 cells. Irofulven caused early (2-5 hours) translocation of the proapoptotic Bax from cytosol to mitochondria followed by the dissipation of mitochondrial membrane potential and cytochrome c release at 4 to 12 hours. These effects preceded caspase activation and during the first 6 hours were not affected by caspase inhibitors. Processing of caspase-9 initiated the caspase cascade at approximately 6 hours and progressed over time. The activation of the caspase cascade provided a positive feedback loop that enhanced Bcl-2-independent translocation and cytochrome c release. General and specific caspase inhibitors abrogated irofulven-induced apoptotic DNA fragmentation with the following order of potency: pan-caspase > or = caspase-9 > caspase-8/6 > caspase-2 > caspase-3/7 > caspase-1/4. Abrogation of caspase-mediated DNA fragmentation failed to salvage irofulven-treated cells from growth inhibition and loss of viability, demonstrating a substantial contribution of a caspase-independent cell death. Monobromobimane, an inhibitor of alternative caspase-independent apoptotic pathway that is mediated by mitochondrial permeability transition, antagonized both apoptosis, measured as phosphatidylserine externalization, and cytotoxicity of irofulven. Collectively, the results indicate that irofulven-induced signaling is integrated at the level of mitochondrial dysfunction. The induction of both caspase-dependent and caspase-independent death pathways is consistent with pleiotropic effects of irofulven, which include targeting of cellular DNA and proteins.     

Helicobacter pylori-induced apoptosis in T cells is mediated by the mitochondrial pathway independent of death receptors

BACKGROUND: Chronic infection with Helicobacter pylori is related to the pathogenesis of the noncardia carcinoma of the stomach. In this study we investigated the mechanisms of H. pylori-induced apoptosis in T lymphocytes, which could explain a mechanism of immune evasion facilitating chronic inflammation of the mucosa and gastric carcinogenesis. MATERIALS AND METHODS: The supernatant of H. pylori culture was used to study the mechanism of apoptosis induction in human leukaemia T cell lines Jurkat and CEM and in primary T cells. The cytotoxin associated gene A (CagA) and vacuolating cytotoxin A (Vac A) positive bacterial strain H. pylori 60190 (CagA(+), VacA(+)) and as a control the less toxic H. pylori strain Tx30a (CagA(-), VacA(-)) were used to produce the supernatant. Cell death was determined by DNA fragmentation and protein expression by Western blot. RESULTS: H. pylori 60190-induced apoptosis was neither blocked by inhibition of the death ligands TRAIL (TNF-related apoptosis-inducing ligand), CD95L/FasL and TNF-alpha (tumour necrosis factor-a) in wild type Jurkat cells nor in FADD(def) (Fas-associated death domain protein) and caspase-8(def) subclones of the Jurkat cell line. Yet, the pancaspase inhibitor zVAD-fmk could inhibit up to 90% of H. pylori-induced apoptosis. Stable transfection of Jurkat wild type cells with Bcl-x(L and) Bcl-2 resulted in marked reduction of H. pylori-induced apoptosis, showing that the mitochondrial pathway is the key regulator. This is supported by the finding that surviving primary human lymphocytes upregulate Bcl-2 when exposed to H. pylori supernatant. CONCLUSIONS: H. pylori-induced apoptosis of T cells is mediated by the mitochondrial pathway and could create a local environment that facilitates life-long infection by immune evasion.     

Fourteen-member macrolides promote the phosphatidylserine receptor-dependent phagocytosis of apoptotic neutrophils by alveolar macrophages

An inflammation of the airway of patients with diffuse panbronchiolitis (DPB), is characterized by dense neutrophil infiltration. Resolution of the inflammation can be achieved by the removal of apoptotic neutrophils by human alveolar macrophages (AM) without liberating neutrophil proteases in the airway. To understand clinical efficacy for the treatment of DPB by 14- or 15-member macrolides, their effects on the phagocytosis of apoptotic neutrophils by AM were examined. Treatment of AM with erythromycin (ERY) or clarithromycin at clinically achievable levels significantly increased the levels of phagocytosis of apoptotic neutrophils. A serum factor was not essential for the enhancement by these 14-member macrolides. Of the antibiotics tested, these effects were specific for the 14-member macrolides and a 15-member macrolide, azithromycin, but not for the 16-member macrolides, clindamycin or beta-lactam antibiotics. The enhanced phagocytosis of apoptotic neutrophils by ERY had no effect on the levels of interleukin-8 or tumor necrosis factor alpha production by lipopolysaccharide-stimulated AM after phagocytosis of the apoptotic neutrophils. The increased phagocytosis of apoptotic neutrophils by ERY was also found to be phosphatidylserine receptor-dependent for AM. These data indicate a novel anti-inflammatory action of 14-member and 15-member macrolides, and suggest that such antibiotics achieve clinical efficacy for patients with DPB, in part, through enhancing the nonphlogistic phagocytosis of apoptotic neutrophils by AM.     

NAC通过不同机制抑制激动剂依赖和非依赖的过表达mGlu1a介导的细胞凋亡

目的 探测N-乙酰半胱氨酸(NAC)对于组成型和诱导型表达mGlu1a所介导的兴奋性毒性的影响。 方法 在过表达mGlu1a的HEK293细胞中,通过免疫印迹法,MTT法,胎盘蓝排斥法,酶联免疫吸附实验,二氯荧光素检测法及HPLC等方法,探测了NAC对mGlu1a下游信号分子活性,细胞活力和凋亡,受体表面表达以及细胞内氧化应激的影响。 结果 发现受体的组成型和诱导型活性通过不同机制,参与了NAC对于mGlu1a所介导的兴奋性毒性的抑制。在以上两种情况下,NAC均可以通过降低ROS调节细胞内氧化还原电势。 结论 在不同生理刺激条件下,mGlu1a的活性对于疾病的发生可能起着不同的作用,尤其是对mGlu1a高表达所产生的效应,为探究与mGluI相关疾病的发生提供了理论依据。     

促红细胞生成素对缺氧乳鼠心肌细胞凋亡及坏死的影响

目的观察促红细胞生成素(EPO)对对缺氧心肌细胞的保护效应及量效关系。方法将当日生乳鼠,局部碘酒酒精消毒后胸骨正中开胸,取心尖前1/2心室肌进行细胞培养。培养4 d后选择细胞生长情况良好的培养瓶(>106个细胞/瓶)分为3组:A,对照组,正常培养;B,缺氧组,缺氧1h/复氧12 h;C,EPO组,缺氧/复氧加EPO干预。EPO组根据不同EPO干预浓度又分为C1,EPO干预浓度0.1 IU/ml;C2,EPO浓度1 IU/ml;C3,EPO干预浓度10 IU/ml。然后以荧光染色-流式细胞仪检测缺氧/复氧后心肌细胞的凋亡及坏死情况。结果缺氧组细胞的凋亡、坏死比率分别为(20.78±2.98)%和(50.10±0.29)%,明显高于EPO各组(P均小于0.01),也明显高于对照组[(2.3±1.09)%和(1.5±0.48)%,P<0.01]。不同浓度EPO浓度干预组间比较,C1组的存活率(40.18±7.49)%低于C2组、C3组(65.56±6.37)%,(62.56±11.32)%,均P<0.01,凋亡率(13.78±3.74)%和坏死率(42.51±5.49)%则明显高于后二者(P<0.05或P<0.01)。C2及C3间各指标差异无统计学意义。结论早期应用EPO可明显减少体外培养的乳鼠心室肌细胞缺氧/复氧后凋亡和坏死的发生。而且EPO在0.1 IU/ml至1 IU/ml浓度范围内其保护作用存在一定的量效关系。     

Novel cell death pathways induced by N-(4-hydroxyphenyl)retinamide: therapeutic implications

We previously reported that N-(4-hydroxyphenyl)retinamide (4HPR) inhibits retinoblastoma tumor growth in a murine model in vivo and kills Y79 retinoblastoma cells in vitro. In this work, we assayed different cell death-related parameters, including mitochondrial damage and caspase activation, in Y79 cells exposed to 4HPR. 4HPR induced cytochrome c release from mitochondria, caspase-3 activation, and oligonucleosomal DNA fragmentation. However, pharmacologic inactivation of caspases by the pan-caspase inhibitor BOC-D-fmk, or specific caspase-3 inhibition by Z-DEVD-fmk, was not sufficient to prevent cell death, as assessed by loss of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction, lactate dehydrogenase release, disruption of mitochondrial transmembrane potential (Deltapsi(m)), and ATP depletion. We found that 4HPR causes lysosomal membrane permeabilization and cytosolic relocation of cathepsin D. Pepstatin A partially rescued cell viability and reduced DNA fragmentation and cytosolic cytochrome c. The antioxidant N-acetylcysteine attenuated cathepsin D relocation into the cytosol, suggesting that lysosomal destabilization is dependent on elevation of reactive oxygen species and precedes mitochondrial dysfunction. Activation of AKT, which regulates energy level in the cell, by the retinal survival facto]r insulin-like growth factor I was impaired and insulin-like growth factor I was ineffective against ATP and Deltapsi(m) loss in the presence of 4HPR. Lysosomal destabilization, associated with mitochondrial dysfunction, was induced by 4HPR also in other cancer cell lines, including PC3 prostate adenocarcinoma and the vascular tumor Kaposi sarcoma KS-Imm cells. The novel finding of a lysosome-mediated cell death pathway activated by 4HPR could have implications at clinical level for the development of combination chemoprevention and therapy of cancer.     

Targeting the mitochondria activates two independent cell death pathways in ovarian cancer stem cells

Cancer stem cells are responsible for tumor initiation and chemoresistance. In ovarian cancer, the CD44+/MyD88+ ovarian cancer stem cells are also able to repair the tumor and serve as tumor vascular progenitors. Targeting these cells is therefore necessary to improve treatment outcome and patient survival. The previous demonstration that the ovarian cancer stem cells are resistant to apoptotic cell death induced by conventional chemotherapy agents suggests that other forms of targeted therapy should be explored. We show in this study that targeting mitochondrial bioenergetics is a potent stimulus to induce caspase-independent cell death in a panel of ovarian cancer stem cells. Treatment of these cells with the novel isoflavone derivative, NV-128, significantly depressed mitochondrial function exhibited by decrease in ATP, Cox-I, and Cox-IV levels, and by increase in mitochondrial superoxide and hydrogen peroxide. This promotes a state of cellular starvation that activates two independent pathways: (i) AMPKα1 pathway leading to mTOR inhibition; and (ii) mitochondrial MAP/ERK kinase/extracellular signal-regulated kinase pathway leading to loss of mitochondrial membrane potential. The demonstration that a compound can specifically target the mitochondria to induce cell death in this otherwise chemoresistant cell population opens a new venue for treating ovarian cancer patients.     

TNF provokes cardiomyocyte apoptosis and cardiac remodeling through activation of multiple cell death pathways

Transgenic mice with cardiac-restricted overexpression of secretable TNF (MHCsTNF) develop progressive LV wall thinning and dilation accompanied by an increase in cardiomyocyte apoptosis and a progressive loss of cytoprotective Bcl-2. To test whether cardiac-restricted overexpression of Bcl-2 would prevent adverse cardiac remodeling, we crossed MHCsTNF mice with transgenic mice harboring cardiac-restricted overexpression of Bcl-2. Sustained TNF signaling resulted in activation of the intrinsic cell death pathway, leading to increased cytosolic levels of cytochrome c, Smac/Diablo and Omi/HtrA2, and activation of caspases -3 and -9. Cardiac-restricted overexpression of Bcl-2 blunted activation of the intrinsic pathway and prevented LV wall thinning; however, Bcl-2 only partially attenuated cardiomyocyte apoptosis. Subsequent studies showed that c-FLIP was degraded, that caspase-8 was activated, and that Bid was cleaved to t-Bid, suggesting that the extrinsic pathway was activated concurrently in MHCsTNF hearts. As expected, cardiac Bcl-2 overexpression had no effect on extrinsic signaling. Thus, our results suggest that sustained inflammation leads to activation of multiple cell death pathways that contribute to progressive cardiomyocyte apoptosis; hence the extent of such programmed myocyte cell death is a critical determinant of adverse cardiac remodeling.     

自噬真核细胞在不动杆菌清除中的机制及诱导巨噬细胞凋亡的蛋白质组织学研究

目的观察自噬真核细胞在不动杆菌清除中的机制及对诱导巨噬细胞凋亡蛋白质组织学的影响。方法取OCR雌性小鼠24只,建立小鼠不动杆菌感染模型,随机分为对照组(n=12)和观察组(n=12)。对照组注射生理盐水,观察组注射自噬真核细胞,测定两组小鼠不动杆菌清除情况及诱导巨噬细胞凋亡的蛋白质组织学情况。结果两组小鼠植入后即刻病灶组织细菌定量比较,差异无统计学意义(P0.05);观察组植入后24、48h病灶组织细菌定量,显著低于对照组(P0.05);观察组小鼠注射自噬真核细胞后肺部组织基本正常,肺泡腔开放,未见异常物质,肺泡壁无明显增厚,且壁内未见炎性细胞浸润。对照组小鼠由于注射生理盐水缺乏不动杆菌清除能力导致肺部可见大量炎性细胞浸润,血管扩张,部分小鼠存在充血现象。结论不动杆菌小鼠体内注射自噬真核细胞能提高机体清除率,诱导巨噬细胞凋亡。     

HSP70 inhibits burn serum-induced apoptosis of cardiomyocytes via mitochondrial and membrane death receptor pathways.

The objective is to determine if Hsp70 is involved in the mechanism by which serum from burn rats induces apoptosis of cardiomyocytes. Cardiomyocytes in primary culture were assigned to the following groups: normal controls, normal rat serum, burn serum, burn serum plus empty vector control, and burn serum plus Hsp70 transfection. Each group, except normal controls, was cultured with the corresponding serum for 2 hours. The empty vector controls and the Hsp70 groups were transfected, respectively, with the empty vector or pcDNA3.1-Hsp70 recombinant plasmid 36 hours previously. Hsp70 protein levels were assessed by Western blot. Apoptotic cells were counted after Hoechst 33258 staining. Apoptosis of cardiomyocytes was also detected by the presence of "ladder" bands in agarose gels following electrophoresis of extracted DNA. Activation of caspase-3, -8, and -9 and Bid cleavage were assessed by Western blot. Hsp70 overexpression inhibited burn serum-induced apoptosis of cardiomyocytes; and burn serum-induced activation of caspases-3, -8, and -9; and Bid cleavage into tBid. Hsp70 inhibits burn serum-induced apoptosis by interfering with death receptor and mitochondrial pathways.     

The inhibition of H1N1 influenza induced apoptosis by sodium selenite through ROS-mediated signaling pathways

The high variability of influenza viruses has made it more difficult for people to cope with influenza. When antigen transformation occurs, even new influenza without preventive vaccines may be produced, which poses a great threat to human health. Selenium is an essential trace element in humans and mammals, and has many biological activities. It has attracted people''s research interest in recent years. In this study, MDCK cells were used as a model to observe the effect of sodium selenite on H1N1 influenza virus. Our research showed that sodium selenite (Na₂SeO₃) has an anti-influenza H1N1 virus effect, and the anti-viral effect of sodium selenite was further demonstrated by caspase-3, AKT, MAPK and p53 signaling pathways. The investigations of the mechanism revealed that the sodium selenite could block H1N1 influenza from infecting MDCK cells through inhibiting the production of ROS. The results demonstrate that selenium supplementation may provide a feasible approach to inhibit the infection of H1N1 influenza virus.

The high variability of influenza viruses has made it more difficult for people to cope with influenza.     

Imbalance of TGF-β1/BMP-7 pathways induced by M2-polarized macrophages promotes hepatocellular carcinoma aggressiveness

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Signalling by proteolysis: death receptors induce apoptosis

Apoptosis, or programmed cell death, is a genetically regulated mechanism with a central role in both metazoan development and homeostasis. Death receptors (Fas, TNFR-2, DR3, and TRAIL receptors) induce apoptosis upon ligation to cognate ligands or ectopic expression. The assembly of a death-inducing signalling complex occurs in a hierarchical manner upon receptor activation. The death domain of the receptor binds to the corresponding domain of the adapter molecule FADD, which in turn recruits the zymogen form of the death protease FLICE (MACH/caspase-8). Upon approximation, FLICE “zymogens” attain a sufficient concentration to self-activate and to trigger the apoptotic pathway. For the first time, a transmembrane receptor directly engaging a protease at the signalling complex and subsequently triggering a proteolytic signalling cascade is described.     

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.