丝氨酸蛋白酶HtrA2/Omi与细胞存亡

HtrA2/Omi是一种寡聚丝氨酸蛋白酶,存在于大部分的正常组织器官中。在最初的研究中发现[1],当细胞受到凋亡刺激时,HtrA2/Omi可由线粒体膜间隙(mitochondrial intermembrane space)释放进入细胞质中,接着出现大量的细胞凋亡性死亡,这些现象表明HtrA2/Omi与细胞死亡之间有着密切的关系[2]。随着近年来研究的不断深入,人们又惊奇地发现,它不仅出现在细胞凋亡的进程中,当细胞面对各种应激环境时,HtrA2/Omi活性和浓度也会上调,以增加细胞对刺激的耐受能力,使细胞得以生存下来。这是一对看似互相矛盾的事实,却更体现出HtrA2/Omi在细胞存亡调…     

Mechanisms regulating neutrophil survival and cell death

Neutrophils not only play a critical role as a first line of defense against bacteria and fungi infections but also contribute to tissue injury associated with autoimmune and inflammatory diseases. Neutrophils are rapidly and massively recruited from the circulation into injured tissues displaying an impressive arsenal of toxic weapons. Although effective in their ability to kill pathogens, these weapons were equally effective to induce tissue damage. Therefore, the inflammatory activity of neutrophils must be regulated with exquisite precision and timing, a task mainly achieved through a complex network of mechanisms, which regulate neutrophil survival. Neutrophils have the shortest lifespan among leukocytes and usually die via apoptosis although new forms of cell death have been characterized over the last few years. The lifespan of neutrophils can be dramatically modulated by a large variety of agents such as cytokines, pathogens, danger-associated molecular patterns as well as by pharmacological manipulation. Recent findings shed light about the complex mechanisms responsible for the regulation of neutrophil survival in different physiological, pathological, and pharmacological scenarios. Here, we provide an updated review on the current knowledge and new findings in this field and discuss novel strategies that could be used to drive the resolution of neutrophil-mediated inflammatory diseases.     

Rho kinase in the regulation of cell death and survival

Rho kinase (ROCK) belongs to a family of serine/threonine kinases that are activated via interaction with Rho GTPases. ROCK is involved in a wide range of fundamental cellular functions, such as contraction, adhesion, migration, and proliferation. Recent studies have shown that ROCK plays an important role in the regulation of apoptosis in various cell types and animal disease models. Two ROCK isoforms, ROCK1 and ROCK2, are assumed to be function redundant, this based largely on kinase construct overexpression and chemical inhibitors (Y27632 and fasudil) which inhibit both ROCK1 and ROCK2. Gene targeting and RNA interference approaches allow further dissection of distinct cellular, physiological, and patho-physiological functions of the two ROCK isoforms. This review, based on recent molecular, cellular, and animal studies, focuses on the current understanding of ROCK signaling in the regulation of apoptosis and highlights new findings from recently generated ROCK-deficient mice.     

T cell signaling: a decision of life and death.

T lymphocytes constitute an essential part of the immune system. Their generation, activation, proliferation but also survival is subject to tight regulation by several extracellular factors including cytokines, MHC-antigen complexes and co-stimulatory ligands. The balanced interplay between these factors determines the fate of the T cell. Both in thymic development and in a peripheral immune response, triggering of the T cell antigen receptor (TCR) through interaction with the MHC-antigen complex can result in T cell proliferation. However, in the absence of co-stimulatory signals from antigen-presenting cells a state of non-responsiveness is induced that is called anergy. In addition, stimulation of the TCR on activated T cells or thymocytes can lead to the induction of apoptosis. Here we will give an overview of the intracellular signal transduction pathways that are activated by the stimuli that dictate the fate of a T cell as they were presented at the International Symposium on soluble HLA antigens held in 1997 in Brussels.     

Mitochondrial involvement in sensory neuronal cell death and survival

Peripheral nerve injuries (PNI) are continuing to be an ever-growing socio-economic burden affecting mainly the young working population and the current clinical treatments to PNI provide a poor clinical outcome involving significant loss of sensation. Thus, our understanding of the underlying factors responsible for the extensive loss of the sensory cutaneous subpopulation in the dorsal root ganglia (DRG) that occurs following injury needs to be improved. The current investigations focus in identifying visual cues of mitochondria-related apoptotic events in the various subpopulations of sensory cutaneous neurons. Sensory neuronal subpopulations were identified using FastBlue retrograde labelling following axotomy. Specialised fluorogenic probes, MitoTracker Red and MitoTracker Orange, were employed to visualise the dynamic changes of the mitochondrial population of neurons. The results reveal a fragmented mitochondrial network in sural neurons following apoptosis, whereas a fused elongated mitochondrial population is present in sensory proprioceptive muscle neurons following tibial axotomy. We also demonstrate the neuroprotective properties of NAC and ALCAR therapy in vitro. The dynamic mitochondrial network breaks down following oxidative exposure to hydrogen peroxide (H₂O₂), but reinitiates fusion after NAC and ALCAR therapy. In conclusion, this study provides both qualitative and quantitative evidence of the susceptibility of sensory cutaneous sub-population in apoptosis and of the neuroprotective effects of NAC and ALCAR treatment on H₂O₂-challenged neurons.     

Involvement of survival motor neuron (SMN) protein in cell death

Infantile spinal muscular atrophy (SMA) is caused by mutations in the survival motor neuron (SMN)1 gene. We investigated the role of human (h) SMN protein on cell death in PC12 and Rat-1 cells. hSMN prolonged cell survival in PC12 cells deprived of trophic support and in Rat-1 cells induced to die by activation of the proto-oncogene c-Myc, to similar magnitude as Bcl-2 or IAP-2. While hSMN was ineffective in inhibiting apoptosis induced by ultraviolet light (UV) or etoposide treatment in proliferating PC12 or Rat-1 cells, a protective effect was observed in terminally NGF/dBcAMP-differentiated PC12 cells. hSMN inhibited the onset of apoptosis in NGF/dBcAMP-deprived or UV-treated co-differentiated PC12 cells by preventing cytochrome c release and caspase-3 activation, indicating that its effects are through suppression of the mitochondrial apoptotic pathway. Expressing hSMN deleted for exon 7 (Delta7) or for exons 6 and 7 (Delta6/7), or with the SMA point mutant Y272C, resulted in loss of survival function. Moreover, these mutants also exhibited pro-apoptotic effects in Rat-1 cells. The localization pattern of full-length hSMN in PC12 and Rat-1 cells was similar to that of endogenous SMN: granular labelling in the cytoplasm and discrete fluorescence spots in the nucleus, some of which co-localized with p80 coilin, the characteristic marker of Cajal bodies. However, cytoplasmic and nuclear aggregates were often seen with hSMNDelta7, whereas the hSMNDelta6/7 mutant showed homogenous nuclear labelling that excluded the nucleolus. Thus, our results show that the C-terminal region is critical in suppression of apoptosis by SMN.     

Redox activation of p21Cip1/WAF1/Sdi1: a multifunctional regulator of cell survival and death

Cell division requires the coordinated assembly of cyclins and cyclin-dependent kinases that promote cell-cycle progression through S phase and mitosis. Two families of cyclin-dependent kinase inhibitors prevent abnormal or premature proliferation by blocking cyclin kinase activity. Expression of the cyclin-dependent kinase inhibitor p21, a member of the Cip/Kip family, increases when cells are damaged. In addition to controlling cell-cycle progression, p21 participates in DNA repair and apoptotic processes. The recent appreciation that p21 regulates cell survival and death implies that it is a master regulator of cell fate. This review discusses how p21 can affect the cellular response to oxidative stress.     

Kinetics of cell death induced in 10T1/2 cells by methyl methanesulfonate and the effects of extracellular calcium on cell death.

The cytotoxic effect of methyl methanesulfonate (MMS) on C3H 10T1/2 cells is characterized by a complex pattern of changes in the permeability of the cell membrane to trypan blue and, therefore, presumably to extracellular calcium. 10T1/2 cells are temporarily, and reversibly, permeable to trypan blue during the initial 30 minutes following exposure to MMS when incubated in the presence of extracellular calcium. By 90-120 minutes after the exposure, the MMS treated cells have restored control of the membrane permeability, and for the next 6-7 hours they exhibit a level of trypan blue uptake comparable to that observed in the untreated cohort population. Between 9 and 15 hours after exposure to MMS the fraction of the population permeable to trypan blue increases rapidly, ultimately approximating the level of cell killing measured concurrently in a colony formation assay. Transient culture in calcium-free medium immediately after exposure to MMS does not protect 10T1/2 cells from cytotoxicity, but incubation in the calcium-free medium does prevent the initial transient episode of permeability to trypan blue observed when the 10T1/2 cells are incubated in calcium-containing medium. These observations suggest that MMS-induced cytotoxicity results from a complex course of events, possibly from damage to an intracellular target rather than from damage to the plasma membrane.     

Inhibition of programmed cell death by cytomegaloviruses

The elimination of infected cells by programmed cell death (PCD) is one of the most ancestral defense mechanisms against infectious agents. This mechanism should be most effective against intracellular parasites, such as viruses, which depend on the host cell for their replication. However, even large and slowly replicating viruses like the cytomegaloviruses (CMVs) can prevail and persist in face of cellular suicide programs and other innate defense mechanisms. During evolution, these viruses have developed an impressive set of countermeasures against premature demise of the host cell. In the last decade, several genes encoding suppressors of apoptosis and necrosis have been identified in the genomes of human and murine CMV (HCMV and MCMV). Curiously, most of the gene products are not homologous to cellular antiapoptotic proteins, suggesting that the CMVs did not capture the genes from the host cell genome. This review summarizes our current understanding of how the CMVs suppress PCD and which signaling pathways they target.     

Cellular FLICE/caspase-8-inhibitory protein as a principal regulator of cell death and survival in human hepatocellular carcinoma

Human hepatocellular carcinomas (HCCs) show resistance to apoptosis mediated by several death receptors. Because cellular FLICE/caspase-8-inhibitory protein (cFLIP) is a recently identified intracellular inhibitor of caspase-8 activation that potently inhibits death signaling mediated by all known death receptors, including Fas, TNF-receptor (TNF-R), and TNF-related apoptosis-inducing ligand receptors (TRAIL-Rs), we investigated the expression and function of cFLIP in human HCCs. We found that cFLIP is constitutively expressed in all human HCC cell lines and is expressed more in human HCC tissues than in nontumor liver tissues. Metabolic inhibitors, actinomycin D (ActD) or cycloheximide (CHX), dramatically rendered HCC cells sensitive to Fas-mediated apoptosis. Neither caspase-8 nor caspase-3 was activated by agonistic anti-Fas antibody alone, but both caspases were activated by Fas stimulation in the presence of ActD or CHX, indicating the importance of caspase-8 inhibitors that are sensitive to metabolic inhibitors. Actually, cFLIP expression was decreased in ActD or CHX treatment. cFLIP down-regulation induced by cFLIP antisense oligodeoxynucleotides sensitized HLE cells to Fas, TNF-R, and TRAIL-R-mediated apoptosis. Furthermore, cFLIP over-expression activated nuclear factor (NF)-kappaB and cFLIP down-regulation attenuated NF-kappaB activation induced by TNF-alpha or TRAIL. Pretreatment with pan-caspase-inhibitor, benzyloxycarbonyl-Val-Ala-Asp (OMe) fluoromethyl ketone (Z-VAD-fmk), restored NF-kappaB activity attenuated by cFLIP down-regulation. cFLIP expression was increased by TNF-alpha, TRAIL, or vascular endothelial growth factor but decreased by wortmannin, indicating that cFLIP expression is regulated by both the NF-kappaB and phosphatidylinostiol-3 kinase (PI-3)/Akt pathways. These results suggest that cFLIP plays an important role in cell survival not simply by inhibiting death-receptor-mediated apoptosis but also by regulating NF-kappaB activation in human HCCs.     

Expression of programmed cell death 1/programmed cell death ligand 1 in the tumor microenvironments of primary gastrointestinal diffuse large B cell lymphomas

Background

Gastrointestinal diffuse large B cell lymphoma (GI DLBCL) is the most common gastrointestinal lymphoma. However, there has not been a comprehensive investigation into the expression patterns of programmed cell death 1 (PD-1) and programmed cell death ligand 1(PD-L1) in GI DLBCL tissues.

Suppression of survival kinases and activation of JNK mediate ethanol-induced cell death in the developing rat brain

Administration of ethanol to immature rat pups during the period in which synaptogenesis occurs triggers extensive apoptotic cell death in the brain. This ethanol-induced cell death is known to be mediated by Bax activation, which is caused by mitochondrial dysfunction. However, little data is available regarding the regulation of survival signaling pathways and their downstream events that lead to Bax activation. Thus, in the present study, we aimed to investigate the effect of ethanol on survival signaling pathways and their downstream events that lead to cell death in the rat brain during the brain developmental period. Ethanol (3 g/kg, 20% in saline) was administered subcutaneously to post-natal 7-day-old rat pups twice at 2-h intervals and the pups were sacrificed at 4 h following the first ethanol injection. Ethanol treatment suppressed the activation of survival kinases, particularly Akt, Erk1/2 and PKAalpha, whereas it increased the activation of JNK. Moreover, dissociation of dephosphorylated Bad from 14-3-3 and the interaction of activated JNK with Bcl-2 were elevated by ethanol treatment. The present study demonstrated that ethanol treatment during the brain developmental period induced mitochondrial dysfunction, which led to cell death by the suppression of survival kinases, Bad release from 14-3-3 and inactivation of Bcl-2 by activated JNK.     

Selective death of T cell receptor gamma/delta+ intraepithelial lymphocytes by apoptosis

In mice, the majority of T cells expressing the gamma/delta T cell receptor (TcR) are found at mucosal surfaces, especially the intestinal epithelium. Here we show that in vitro, the majority of TcR gamma/delta+ intraepithelial lymphocytes, but not TcR alpha/beta+ intraepithelial lymphocytes, undergo rapid and selective programmed cell death by apoptosis.     

The role of autophagy in mediating cell survival and death during ischemia and reperfusion in the heart

Autophagy is a major mechanism for degrading long-lived cytosolic proteins and the only known pathway for degrading organelles. Autophagy is activated by many forms of stress, including nutrient and energy starvation, oxidative stress, mitochondrial dysfunction, endoplasmic reticulum stress, and infections. Although autophagy recycles amino acids and fatty acids to produce energy and removes damaged organelles, thereby playing an essential role in cell survival, inappropriate activation of autophagy leads to cell death. In the heart, activation of autophagy can be observed in response to nutrient starvation, ischemia/reperfusion, and heart failure. In this review, the signaling mechanism and the functional significance of autophagy during myocardial ischemia and reperfusion are discussed.     

Con A activates an Akt/PKB dependent survival mechanism to modulate TCR induced cell death in double positive thymocytes

While low avidity ligation of the T cell receptor (TCR) leads to positive selection and further maturation of developing thymocytes providing the immune system with mature CD4(+) and CD8(+) (single positive) T cells, high avidity ligation triggers negative selection by apoptotic cell death and therefore the TCR repertoire is purged of autoreactive T cells. On peripheral T cells, however, high avidity ligation of the TCR triggers activation and survival not death. In the present study we used concanavalin A (Con A) and alpha-CD3 epsilon antibody to investigate a possible survival mechanism in connection with TCR ligation. Con A and alpha-CD3 epsilon were used in the study for the following reasons: (1) they both mimic the effects of high avidity TCR ligation by activating peripheral T cells, and (2) they trigger distinctively different physiological changes in developing thymocytes. While Con A supports events associated with cellular survival, alpha-CD3 epsilon induces apoptotic cell death. In our experimental system the TCR was cross-linked by Con A and alpha-CD3 epsilon in thymocytes of major histocompatibility complex (MHC) deficient thymus organ cultures, where signals from the TCR can be triggered on zero background signal level. We have found that TCR cross-linking by Con A and not by alpha-CD3 epsilon decreases the gene and protein expression of the pro-apoptotic molecule, Bad; and that Con A is capable of the activation of the survival signalling pathway including protein kinase B (Akt/PKB) independently of phosphatidyl inositol kinase (PI3K).     

Induction of cell death by chimeric L-selectin-Fas receptors

In the present study, we have established a system where engagement of an adhesion molecule triggers a death signal into cells. L-selectin, which is a well characterized adhesion receptor involved in the initial adhesion between lymphocyte and endothelium, was fused to the intracellular domain of an apoptosis-inducing molecule, Fas. Ligation of the chimeric receptors with a carbohydrate ligand for L-selectin, fucoidin or a mAb that recognizes the lectin domain of L-selectin, induced apoptosis in receptor-expressing cells. However, ligation with an anti-L-selectin mAb reactive with a non-ligand binding site did not induce apoptosis, indicating that stimulation through the lectin domain of L-selectin in the chimeric receptor leads to signal delivery. Upon activation L-selectin shows a unique proteolytic cleavage at the membrane proximal site on the extracellular (EC) domain, of which the significance is also unclear. We found that truncations in the EC domain which abrogate the proteolytic cleavage of L-selectin did not influence induction of apoptosis, suggesting that the cleavage on the EC domain itself is not important for the signaling function of the chimeric receptor. This is the first demonstration that an adhesion signal can be converted to a signal that leads to apoptotic cell death.      

An interaction between type 1 and type 2 programmed cell death and clonogenic survival

We suggest two additional reasons why current, non-surgical therapies for most solid, epithelial-derived cancers can lack effectiveness. Studies with panc-1 human pancreatic cancer cells cultured with actinomycin D and/or MK 886 indicate firstly, that type 2 (intrinsic, autophagic, mitochondrial-dependent, MK 886-induced) programmed cell death is less effective than the type 1 (apoptotic, extrinsic, ligand-dependent, actinomycin D-induced) form in reducing the number of residual clonogenic cells, and secondly, that activation of cellular suicide during their combined culture results in a greater number of residual clonogenic cells compared with either agent alone. HYPOTHESIS: Based on results from the culture of panc-1 cells with MK 886 and/or actinomycin D, we suggest that in this system, and possibly in others: (a) type 2 programmed cell death is a less effective inhibitor of residual cells with clonogenic potential, and (b) activation together of both forms of PCD increases the number of residual clonogenic cells.     

Inhibition of programmed cell death by cyclosporin A; preferential blocking of cell death induced by signals via TCR/CD3 complex and its mode of action.

Cyclosporin A (CsA) is reported to inhibit programmed cell death. We confirmed this by using T-cell hybridomas which are inducible to programmed cell death by activation with immobilized anti-CD3 antibody or with anti-Thy 1.2 antibody. Cell death and DNA fragmentation, characteristic features of programmed cell death, were almost completely blocked by CsA or FK506. To investigate whether CsA inhibits only the cell death through the signals via the TCR/CD3 complex or all of the programmed cell death induced by various reagents, we further established CD4+8+ thymic lymphomas which result in programmed cell death after activation with calcium ionophore, dexamethasone, cyclic AMP or anti-CD3 antibody. It was revealed that CsA could block only the cell death mediated by the TCR/CD3 complex. For the clarification of the site of action of CsA, Ca2+ influx and endocytosis of receptors after stimulation with anti-CD3 antibody were monitored in the presence of CsA, and no significant effects of CsA were observed. Furthermore, prevention of cell death was examined by adding CsA at various periods of time after initiation of culture. CsA was found to exert its effect even when added after 4 h of cultivation, and the kinetic pattern of suppression was similar to that of the suppressive effect on IL-2 production. These observations indicate that in the events of programmed cell death, the major site of action of CsA will not be the inhibition of the immediate membrane events after activation of the TCR/CD3 complex but rather the interference in the function of molecules that transmit signals between membrane events and the activation of genes in the nucleus.