Caspase-independent cell death in T lymphocytes

Pro-apoptotic effect of maize lipid transfer protein on mammalian mitochondria

To assess the effect of lipids and lipid exchange in the pro-apoptotic release of cytochrome c, we investigated the ability of a plant lipid transfer protein (LTP) to initiate the apoptotic cascade at the mitochondrial level. The results show that maize LTP is able to induce cytochrome c release from the intermembrane space of mouse liver mitochondria without significant mitochondrial swelling, similarly to mouse full-length Bid. This effect is influenced by the presence of specific lipids, since addition of lysolipids like lysophosphatidylcholine strongly stimulates the LTP-induced release of cytochrome c while it is inhibited by removal of endogenous free lipids with a complete suppression of the LTP-induced release of cytochrome c. The results are discussed in light of the possible role of lipid exchange in apoptosis.

Cell death in pancreatitis: caspases protect from necrotizing pancreatitis

Mechanisms of cell death in pancreatitis remain unknown. Parenchymal necrosis is a major complication of pancreatitis; also, the severity of experimental pancreatitis correlates directly with necrosis and inversely with apoptosis. Thus, shifting death responses from necrosis to apoptosis may have a therapeutic value. To determine cell death pathways in pancreatitis and the possibility of necrosis/apoptosis switch, we utilized the differences between the rat model of cerulein pancreatitis, with relatively high apoptosis and low necrosis, and the mouse model, with little apoptosis and high necrosis. We found that caspases were greatly activated during cerulein pancreatitis in the rat but not mouse. Endogenous caspase inhibitor X-linked inhibitor of apoptosis protein (XIAP) underwent complete degradation in the rat but remained intact in the mouse model. Furthermore, XIAP inhibition with embelin triggered caspase activation in the mouse model, implicating XIAP in caspase blockade in pancreatitis. Caspase inhibitors decreased apoptosis and markedly stimulated necrosis in the rat model, worsening pancreatitis parameters. Conversely, caspase induction with embelin stimulated apoptosis and decreased necrosis in mouse model. Thus, caspases not only mediate apoptosis but also protect from necrosis in pancreatitis. One protective mechanism is through degradation of receptor-interacting protein (RIP), a key mediator of "programmed" necrosis. We found that RIP was cleaved (i.e. inactivated) in the rat but not the mouse model. Caspase inhibition restored RIP levels; conversely, caspase induction with embelin triggered RIP cleavage. Our results indicate key roles for caspases, XIAP, and RIP in the regulation of cell death in pancreatitis. Manipulating these signals to change the pattern of death responses presents a therapeutic strategy for treatment of pancreatitis.

Molecular basis of programmed cell death involved in neurodegeneration

Rapid progress in understanding the molecular basis of neurodegeneration has been tightly linked with recent discoveries in the field of programmed cell death (PCD). Analysis of PCD in neuronal demise has led to identification of several associated phenomena, such as re-initiation of the cell cycle and the key role of oxidative stress, although putative causal relationships between these events are still debatable. These issues are reviewed here in the context of acute and chronic neurodegenerative processes. In addition, newly emerging concepts concerning cell-cycle re-initiation are discussed in terms of their potential impact on the development of more effective therapeutic strategies.

AIF and endoG translocation in noise exposure induced hair cell death

Activation of caspases is a key element in the apoptotic process. However, mitochondria also play an important role via the release of proapoptotic proteins. This study investigated the roles of mitochondria-related apoptosis inducing factor (AIF) and endonuclease G (endoG), mitochondrion-specific nucleases, as well as caspase-3, an important mediator of apoptosis, in noise exposure induced hair cell death. Guinea pigs were exposed for 4h/day to broadband noise at 122 dB SPL for 2 days. After the noise exposure, the cochleae were examined for the activity of caspase-3 with carboxyfluorescein-labeled fluoromethyl ketone (FMK)-peptide inhibitors. The cochleae were further examined for AIF and endoG translocation from the mitochondria by immunohistochemistry. Noise exposure triggered activation of caspase-3 in apoptotic hair cells. In the normal organ of Corti, AIF and endoG were co-localized to the mitochondria. After noise exposure, AIF translocated into the nuclei of apoptotic and necrotic hair cells. The translocation of endoG from mitochondria into the nucleus was also found in apoptotic OHCs. These findings indicate that mitochondria-released proapoptotic proteins, AIF and endoG, are important factors in a noise-induced hair cell death pathway.

Lysosomes and autophagy in cell death control

Lysosomal hydrolases participate in the digestion of endocytosed and autophagocytosed material inside the lysosomal/autolysosomal compartment in acute cell death when released into the cytosol and in cancer progression following their release into the extracellular space. Lysosomal alterations are common in cancer cells. The increased expression and altered trafficking of lysosomal enzymes participates in tissue invasion, angiogenesis and sensitization to the lysosomal death pathway. But lysosomal heat-shock protein 70 locally prevents lysosomal-membrane permeabilization. Similarly, alterations in the autophagic compartment are linked to carcinogenesis and resistance to chemotherapy. Targeting these pathways might constitute a novel approach to cancer therapy.

The Anti-Death Machinery in IKK/NF-κB Signaling

The most extensively studied function of NF-kappaB is its ability to promote cell survival through induction of target genes, whose products inhibit various aspects of the apoptotic machinery in both normal and malignant cells. Recent studies, however, indicate that NF-kappaB activation can also suppress programmed necrosis through induction of genes encoding anti-oxidant proteins. Since tumor cells often use NF-kappaB pathway as a shield to escape the killing of conventional anti-cancer therapies, intervention of IKK/NF-kappaB signaling would be a promising option to improve the efficacy of cancer treatment.

The cathepsin B death pathway contributes to TNF plus IFN-gamma-mediated human endothelial injury

Vascular endothelial cells are primary targets of cytokine-induced cell death leading to tissue injury. We previously reported that TNF in combination with LY294002, a PI3K inhibitor, activates caspase-independent cell death initiated by cathepsin B (Cat B) in HUVEC. We report that TNF in the presence of IFN-gamma activates Cat B as well as a caspase death pathway in both HUVEC and human dermal microvascular endothelial cells, but only activates caspase-mediated death in HeLa cells and human embryonic kidney (HEK)293 cells. Like LY294002, IFN-gamma triggers Cat B release from lysosomes in HUVEC. Cat B-triggered death involves mitochondria, indicated by release of cytochrome c, loss of mitochondrial membrane potential and inhibition of death by overexpressed Bcl-2. Cat B effects on mitochondria do not depend upon Bid cleavage. Unexpectedly, overexpression of a dominant negative mutated form of Fas-associated death domain protein (FADD), which blocks caspase activation by TNF, potentiates TNF activation of Cat B and cell death in HUVEC. Similarly, mutant Jurkat cells lacking FADD also show increased susceptibility to TNF-induced Cat B-dependent cell death. These observations suggest that the Cat B death pathway is cell type-specific and may contribute to cytokine-mediated human tissue injury and to the embryonic lethality of FADD gene disruption in mice.

Cardiolipin and its metabolites move from mitochondria to other cellular membranes during death receptor-mediated apoptosis

We previously reported that during death receptor-mediated apoptosis, cardiolipin (CL) relocates to the cell surface, where it reacts with autoantibodies from antiphospholipid syndrome sera. Here, we analysed the intracellular distribution of CL and its metabolites during the early phase of cell death signalling triggered by Fas stimulation in U937 cells and mouse liver. We found a redistribution of mitochondrial CL to the cell surface by using confocal microscopy and flow cytometry. Mass spectrometry revealed that CL and its metabolites relocated from mitochondria to other intracellular organelles during apoptosis, with a conversion into non-mitochondrial lipids. Concomitantly, cytosolic Bid relocated to the light membranes comprised in fraction P100, including the plasma membrane and associated vesicular systems. A direct Bid-CL interaction was demonstrated by the observation that CL and monolysoCL coimmunoprecipitated with Bid especially after Fas stimulation, suggesting a dynamic interaction of the protein with CL and its metabolites.

A novel anti-human DR5 monoclonal antibody with tumoricidal activity induces caspase-dependent and caspase-independent cell death

Like anti-Fas monoclonal antibodies, some monoclonal antibodies against tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors have tumoricidal activity too. In this article we report a novel mouse anti-human DR5 monoclonal antibody, AD5-10, that induces apoptosis of various tumor cell lines in the absence of second cross-linking in vitro and showed strong tumoricidal activity in vivo. AD5-10 does not compete with TRAIL for binding to DR5 and synergizes with TRAIL to induce apoptosis of tumor cells. AD5-10 induces both caspase-dependent and caspase-independent cell death in Jurkat cells, whereas TRAIL induces only caspase-dependent cell death. We show for the first time that DR5 can mediate caspase-independent cell death, and DR5 can mediate distinct cell signals when interacting with different extracellular proteins. Studies on AD5-10 help us to understand more on the functions of DR5 and may provide new ideas for cancer immunotherapy.

The apoptosis inhibitory domain of FE65-like protein 1 regulates both apoptotic and caspase-independent programmed cell death mediated by tumor necrosis factor

Tumor necrosis factor (TNF) can induce caspase-dependent (apoptotic) and caspase-independent pathways to programmed cell death (PCD). Here, we demonstrate that stable transfection of a cDNA encompassing the C-terminal apoptosis inhibitory domain (AID) of FE65-like protein 1 into mouse L929 fibrosarcoma cells protects from caspase-independent as well as from apoptotic PCD induced by TNF. We show that the AID does not protect from caspase-independent PCD elicited by 1-methyl-3-nitro-1-nitrosoguanidine, suggesting that the AID might prevent cell death by affecting assembly of the death inducing signaling complex of the 55 kDa TNF receptor or clustering of the receptor itself. Interference with caspase-independent PCD mediated by the sphingolipid ceramide further increases protection conferred by the AID, as does the antioxidant butylated hydroxyanisole, implicating ceramide and reactive oxygen species as potential factors interacting with caspase-independent PCD regulated by the AID.

Tumour necrosis factor-induced death of adult human oligodendrocytes is mediated by apoptosis inducing factor

Tumour necrosis factor (TNF)-induced death of oligodendrocytes, the cell type targeted in multiple sclerosis, is mediated by TNF receptor p55 (TNFR-p55). The ligation of TNFR-p55 induces several signal transduction pathways; however, the precise mechanism involved in human oligodendrocyte (hOL) death is unknown. We defined that TNF-induced death of hOLs is non-caspase dependent, as evidenced by lack of generation of caspases 8, 1 and 3 active subunits; lack of cleavage of caspases 1 and 3 fluorogenic substrates; and lack of hOL death inhibition by the general caspase inhibitor, ZVAD.FMK. Electrophoresis of TNF-exposed hOL DNA revealed large-scale DNA fragmentation characteristic of apoptosis-inducing factor (AIF)-mediated cell death, and co-localization experiments showed that AIF translocation to the nucleus occurred upon exposure to TNF. AIF depletion by an antisense strategy prevented TNF-induced hOL death. These results indicate that TNF-induced death of hOLs is dependent on AIF, information of significance for the design strategies to protect hOLs during immune-mediated demyelination.

Novel inosine monophosphate dehydrogenase inhibitor VX-944 induces apoptosis in multiple myeloma cells primarily via caspase-independent AIF/Endo G pathway

Inosine monophosphate dehydrogenase (IMPDH) is a rate-limiting enzyme required for the de novo synthesis of guanine nucleotides from IMP. VX-944 (Vertex Pharmaceuticals, Cambridge, MA, USA) is a small-molecule, selective, noncompetitive inhibitor directed against human IMPDH. In this report, we show that VX-944 inhibits in vitro growth of human multiple myeloma (MM) cell lines via induction of apoptosis. Interleukin-6, insulin-like growth factor-1, or co-culture with bone marrow stromal cells (BMSCs) do not protect against VX-944-induced MM cell growth inhibition. VX-944 induced apoptosis in MM cell lines with only modest activation of caspases 3, 8, and 9. Furthermore, the pan-caspase inhibitor z-VAD-fmk did not inhibit VX-944-induced apoptosis and cell death. During VX-944-induced apoptosis, expressions of Bax and Bak were enhanced, and both apoptosis-inducing factor (AIF) and endonuclease G (Endo G) were released from the mitochondria to cytosol, suggesting that VX-944 triggers apoptosis in MM cells primarily via a caspase-independent, Bax/AIF/Endo G pathway. Importantly, VX-944 augments the cytotoxicity of doxorubicin and melphalan even in the presence of BMSCs. Taken together, our data demonstrate a primarily non-caspase-dependent apoptotic pathway triggered by VX-944, thereby providing a rationale to enhance MM cell cytotoxicity by combining this agent with conventional agents which trigger caspase activation.

Cellular integrity plus: organelle-related and protein-targeting functions of intermediate filaments

Intermediate filament proteins (IFs) maintain cell and tissue integrity, based on evidence of their polymerization and mechanical properties, abundance and disease-associated phenotypes. This 'traditional' function is now augmented by organelle-related and protein-targeting roles. Mitochondrial location and function depend on intact IFs, as demonstrated for desmin, keratins and neurofilaments. Golgi positioning is regulated by several IFs, and endosomal/lysosomal protein distribution by vimentin. IFs dramatically affect nuclear function and shape and play a role in subcellular and membrane targeting of proteins. These functions have been noted in tissues but in some cases only in cell culture. The IF-related organelle-specific and protein-targeting roles, which are likely interrelated, provide functions beyond cell scaffolding and integrity and contribute to the cytoprotective and tissue-specific functions of IF proteins.

Beyond apoptosis: nonapoptotic cell death in physiology and disease

Apoptosis is a morphologically defined form of programmed cell death (PCD) that is mediated by the activation of members of the caspase family. Analysis of death-receptor signaling in lymphocytes has revealed that caspase-dependent signaling pathways are also linked to cell death by nonapoptotic mechanisms, indicating that apoptosis is not the only form of PCD. Under physiological and pathological conditions, cells demonstrate a high degree of flexibility in cell-death responses, as is reflected in the existence of a variety of mechanisms, including necrosis-like PCD, autophagy (or type II PCD), and accidental necrosis. In this review, we discuss recent data suggesting that canonical apoptotic pathways, including death-receptor signaling, control caspase-dependent and -independent cell-death pathways.Key words: apoptosis, necrosis, nonapoptotic programmed cell death, death receptors, ceramides.

IKK/NF-kappaB signaling: balancing life and death--a new approach to cancer therapy

IkappaB kinase/NF-kappaB (IKK/NF-kappaB) signaling pathways play critical roles in a variety of physiological and pathological processes. One function of NF-kappaB is promotion of cell survival through induction of target genes, whose products inhibit components of the apoptotic machinery in normal and cancerous cells. NF-kappaB can also prevent programmed necrosis by inducing genes encoding antioxidant proteins. Regardless of mechanism, many cancer cells, of either epithelial or hematopoietic origin, use NF-kappaB to achieve resistance to anticancer drugs, radiation, and death cytokines. Hence, inhibition of IKK-driven NF-kappaB activation offers a strategy for treatment of different malignancies and can convert inflammation-induced tumor growth to inflammation-induced tumor regression.

Prostaglandin D2 induces programmed cell death in Trypanosoma brucei bloodstream form

African trypanosomes produce some prostanoids, especially PGD2, PGE2 and PGF2alpha (Kubata et al. 2000, J. Exp. Med. 192: 1327-1338), probably to interfere with the host's physiological response. However, addition of prostaglandin D2 (but not PGE2 or PGF2alpha) to cultured bloodstream form trypanosomes led also to a significant inhibition of cell growth. Based on morphological alterations and specific staining methods using vital dyes, necrosis and autophagy were excluded. Here, we report that in bloodstream form trypanosomes PGD2 induces an apoptosis-like programmed cell death, which includes maintenance of plasma membrane integrity, phosphatidylserine exposure, loss of mitochondrial membrane potential, nuclear chromatin condensation and DNA degradation. The use of caspase inhibitors cannot prevent the cell death, indicating that the process is caspase-independent. Based on these results, we suggest that PGD2-induced programmed cell death is part of the population density regulation as observed in infected animals.

Zonal necrosis prevented by transduction of the artificial anti-death FNK protein

Protection of cells from necrosis would be important for many medical applications. Here, we show protein transduction domain (PTD)-FNK therapeutics based on protein transduction to prevent necrosis and acute hepatic injury with zonal death induced by carbon tetrachloride (CCl4). PTD-FNK is a fusion protein comprising the HIV/Tat PTD and FNK, a gain-of-function mutant of anti-apoptotic Bcl-x(L). PTD-FNK protected hepatoma HepG2 from necrotic death induced by CCl4, and additionally, increased the apoptotic population among cells treated with CCl4. A concomitant treatment with a pan-caspase inhibitor Z-VAD-FMK (N-benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone), which alone could not prevent the necrosis, protected these cells from the apoptosis. When pre-injected intraperitoneally, PTD-FNK markedly reduced zonal liver necrosis caused by CCl4. Moreover, injection of PTD-FNK accompanied by Z-VAD-FMK suppressed necrotic injury even after CCl4 administration. These results suggest that PTD-FNK has great potential for clinical applications to prevent cell death, whether from apoptosis or necrosis, and organ failure.

Up-regulation of lysosomal cathepsin L and autophagy during neuronal death induced by reduced serum and potassium

Serum and potassium deprivation-induced neuronal death on the primary culture of rat cerebellar granule neurons is being widely used as an in vitro model of neurodegeneration and neuronal apoptosis. In our experiments, serum and potassium deprivation for 12 h induced neuronal death in approximately 20% of cerebellar granule neurons as demonstrated by Trypan Blue assay. Neuronal death was accompanied by a transient increase in the intralysosomal cathepsin L activity, which preceded neuronal death. During this time, the lysosomal membrane integrity remained preserved and no leakage of cathepsin L into the cytosol was seen. Ultrastructural analysis revealed the appearance of multiple vacuoles and autophagosomes in the cytoplasmatic compartment of serum- and potassium-deprived granule neurons. Addition of selective cathepsin L inhibitors or of the autophagy inhibitor 3-methyladenine provided partial protection against serum and potassium deprivation-induced death. Our data also show that combining cathepsin L inhibitors and caspase-3 inhibitors leads to a synergistic neuroprotective effect against serum and potassium deprivation. The results of the current study suggest that activation of the autophagosomal--lysosomal compartment plays an important role in neuronal death induced by serum and potassium deprivation in cultured cerebellar granule cells.

A virus essential for insect host-parasite interactions encodes cystatins

Cotesia congregata is a parasitoid wasp that injects its eggs in the host caterpillar Manduca sexta. In this host-parasite interaction, successful parasitism is ensured by a third partner: a bracovirus. The relationship between parasitic wasps and bracoviruses constitutes one of the few known mutualisms between viruses and eukaryotes. The C. congregata bracovirus (CcBV) is injected at the same time as the wasp eggs in the host hemolymph. Expression of viral genes alters the caterpillar's immune defense responses and developmental program, resulting in the creation of a favorable environment for the survival and emergence of adult parasitoid wasps. Here, we describe the characterization of a CcBV multigene family which is highly expressed during parasitism and which encodes three proteins with homology to members of the cystatin superfamily. Cystatins are tightly binding, reversible inhibitors of cysteine proteases. Other cysteine protease inhibitors have been described for lepidopteran viruses; however, this is the first description of the presence of cystatins in a viral genome. The expression and purification of a recombinant form of one of the CcBV cystatins, cystatin 1, revealed that this viral cystatin is functional having potent inhibitory activity towards the cysteine proteases papain, human cathepsins L and B and Sarcophaga cathepsin B in assays in vitro. CcBV cystatins are, therefore, likely to play a role in host caterpillar physiological deregulation by inhibiting host target proteases in the course of the host-parasite interaction.

Caspase-independent cell death

Caspase activation has been frequently viewed as synonymous with apoptotic cell death; however, caspases can also contribute to processes that do not culminate in cell demise. Moreover, inhibition of caspases can have cytoprotective effects. In a number of different models, caspase inhibition does not maintain cellular viability and instead shifts the morphology of death from apoptosis to nonapoptotic pathways. Here, we explore the contribution of caspases to cell death, either as upstream signals or as downstream effectors contributing to apoptotic morphology, as well as alternative strategies for cell death inhibition. Such alternative strategies may either target catabolic hydrolases or be aimed at preventing mitochondrial membrane permeabilization and its upstream triggers.

Induction of reactive oxygen intermediates-dependent programmed cell death in human malignant ex vivo glioma cells and inhibition of the vascular endothelial growth factor production by taurolidine

OBJECT

Taurolidine, a derivative of the amino acid taurin, was recently found to display a potent antineoplastic effect both in vitro and in vivo. The authors therefore initiated studies to assess the potential antineoplastic activity of taurolidine in human glioma cell lines and in ex vivo malignant cell cultures. They also studied the mechanisms that induce cell death and the impact of taurolidine on tumor-derived vascular endothelial growth factor (VEGF) production.

METHODS

Cytotoxicity and clonogenic assays were performed using crystal violet staining. In the cytotoxicity assay 100% of glioma cell lines (eight of eight) and 74% of ex vivo glioma cultures (14 of 19) demonstrated sensitivity to taurolidine, with a mean median effective concentration (EC50) of 51 +/- 28 microg/ml and 56 +/- 23 microg/ml, respectively. Colony formation was inhibited by taurolidine, with a mean EC50 of 7 +/- 3 microg/ml for the cell lines and a mean EC50 of 3.5 +/- 1.7 microg/ml for the ex vivo glioma cultures. On observing this high activity of taurolidine in both assays, the authors decided to evaluate its cell death mechanisms. Fragmentation of DNA, externalization of phosphatidylserine, activation of poly(adenosine diphosphate-ribose) polymerase, loss of the mitochondrial membrane potential followed by a release of apoptosis-inducing factor, and typical apoptotic features were found after taurolidine treatment. Cell death was preceded by the generation of reactive O2 intermediates, which was abrogated by N-acetylcysteine but not by benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone. Moreover, taurolidine also induced suppression of VEGF production on the protein and messenger RNA level, as shown by an enzyme-linked immunosorbent assay and by reverse transcription-polymerase chain reaction.

CONCLUSIONS

Given all these findings, taurolidine may be a promising new agent in the treatment of malignant gliomas; it displays a combination of antineoplastic and antiangiogenic activities, inducing tumor cell apoptosis and inhibiting tumor-derived VEGF production.

Soluble MHC-peptide complexes induce rapid death of CD8+ CTL

Soluble MHC-peptide (pMHC) complexes, commonly referred to as tetramers, are widely used to enumerate and to isolate Ag-specific CD8(+) CTL. It has been noted that such complexes, as well as microsphere- or cell-associated pMHC molecules compromise the functional integrity of CTL, e.g., by inducing apoptosis of CTL, which limits their usefulness for T cell sorting or cloning. By testing well-defined soluble pMHC complexes containing linkers of different length and valence, we find that complexes comprising short linkers (i.e., short pMHC-pMHC distances), but not those containing long linkers, induce rapid death of CTL. This cell death relies on CTL activation, the coreceptor CD8 and cytoskeleton integrity, but is not dependent on death receptors (i.e., Fas, TNFR1, and TRAILR2) or caspases. Within minutes of CTL exposure to pMHC complexes, reactive oxygen species emerged and mitochondrial membrane depolarized, which is reminiscent of caspase-independent T cell death. The morphological changes induced during this rapid CTL death are characteristic of programmed necrosis and not apoptosis. Thus, soluble pMHC complexes containing long linkers are recommended to prevent T cell death, whereas those containing short linkers can be used to eliminate Ag-specific CTL.

Immature CD4−CD103+Rat Dendritic Cells Induce Rapid Caspase-Independent Apoptosis-Like Cell Death in Various Tumor and Nontumor Cells and Phagocytose Their Victims

We previously reported the characterization of a MHC class II(low) CD4- CD103+ (CD4-) subset of dendritic cells (DC) in rat spleen that exhibit a Ca2+-, Fas ligand-, TRAIL- and TNF-alpha-independent cytotoxic activity against specific targets in vitro. In this study, we demonstrate that this DC subset was also found in lymph nodes. Freshly extracted and, therefore, immature CD4- DC exhibited a potent cytotoxic activity against a large panel of tumor cell lines as well as primary endothelial cells. The cytotoxic activity of immature CD4- DC required cell-to-cell contact and de novo protein expression. CD4- DC-mediated cell death resembled apoptosis, as evidenced by outer membrane phosphatidylserine exposure and nuclear fragmentation in target cells, but was caspase as well as Fas-associated death domain and receptor-interacting protein independent. Bcl-2 overexpression in target cells did not protect them against DC-mediated cell death. Immature CD4- DC phagocytosed efficiently apoptotic cells in vitro and, therefore, rapidly and specifically engulfed their victims following death induction. Maturation induced a dramatic down-regulation of the killing and phagocytic activities of CD4- DC. In contrast, CD4+ DC were both unable to kill target cells and to phagocytose apoptotic cells in vitro. Taken together, these data indicate that rat immature CD4- CD103+ DC mediate an unusual cytotoxic activity and can use this function to efficiently acquire Ag from live cells.

Cell death independent of caspases: a review

Patterns of cell death have been divided into apoptosis, which is actively executed by specific proteases, the caspases, and accidental necrosis. However, there is now accumulating evidence indicating that cell death can occur in a programmed fashion but in complete absence and independent of caspase activation. Alternative models of programmed cell death (PCD) have therefore been proposed, including autophagy, paraptosis, mitotic catastrophe, and the descriptive model of apoptosis-like and necrosis-like PCD. Caspase-independent cell death pathways are important safeguard mechanisms to protect the organism against unwanted and potential harmful cells when caspase-mediated routes fail but can also be triggered in response to cytotoxic agents or other death stimuli. As in apoptosis, the mitochondrion can play a key role but also other organelles such as lysosomes and the endoplasmic reticulum have an important function in the release and activation of death factors such as cathepsins, calpains, and other proteases. Here we review the various models of PCD and their death pathways at molecular and organelle level and discuss the relevance of the growing knowledge of caspase-independent cell death pathways for cancer.

Autophagy: dual roles in life and death?

Autophagy is an evolutionarily conserved mechanism for the degradation of cellular components in the cytoplasm, and serves as a cell survival mechanism in starving cells. Recent studies indicate that autophagy also functions in cell death, but the precise role of this catabolic process in dying cells is not clear. Here I discuss the possible roles for autophagy in dying cells and how understanding the relationship between autophagy, cell survival and cell death is important for health and development.

Discovery of a novel small molecule, 1-ethoxy-3-(3,4-methylenedioxyphenyl)-2-propanol, that induces apoptosis in A549 human lung cancer cells

A novel small molecule, 1-ethoxy-3-(3,4-methylenedioxyphenyl)-2-propanol (EOD), was synthesized in our laboratory. Previously, we reported pharmacological properties of EOD, triggering apoptosis in Human umbilical vein endothelial cells (HUVECs). Here, we further investigated the effects of EOD on the growth of A549 human lung cancer cells. EOD treatment induced apoptosis in A549 cells via up-regulating the expression of P53 protein, blocking cell cycle partly at G1 phase, and ultimately activating caspase-3. In contrast, caspase-8 might be irrelevant to EOD-triggered apoptosis. This study indicated that EOD might be a potential chemopreventive agent for lung cancer. The work would encourage us to add more novel compounds to our 'library' of small molecules derived through modern synthetic organic chemistry, and would drive us to determine the proteins that the compounds target.

Galectin-1 induces nuclear translocation of endonuclease G in caspase- and cytochrome c-independent T cell death

Galectin-1, a mammalian lectin expressed in many tissues, induces death of diverse cell types, including lymphocytes and tumor cells. The galectin-1 T cell death pathway is novel and distinct from other death pathways, including those initiated by Fas and corticosteroids. We have found that galectin-1 binding to human T cell lines triggered rapid translocation of endonuclease G from mitochondria to nuclei. However, endonuclease G nuclear translocation occurred without cytochrome c release from mitochondria, without nuclear translocation of apoptosis-inducing factor, and prior to loss of mitochondrial membrane potential. Galectin-1 treatment did not result in caspase activation, nor was death blocked by caspase inhibitors. However, galectin-1 cell death was inhibited by intracellular expression of galectin-3, and galectin-3 expression inhibited the eventual loss of mitochondrial membrane potential. Galectin-1-induced cell death proceeds via a caspase-independent pathway that involves a unique pattern of mitochondrial events, and different galectin family members can coordinately regulate susceptibility to cell death.

Structure–activity relationship of N-methyl-bisindolylmaleimide derivatives as cell death inhibitors

A series of N-methyl-bisindolylmaleimide derivatives was synthesized and evaluated as cell death inhibitors. N-Methyl-2-[1-(3-aminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)maleimide (21) was the most potent inhibitor of H2O2-induced necrotic death of human leukemia HL60 cells among them.

Molecular mechanisms of glucocorticoids in the control of inflammation and lymphocyte apoptosis

The immune system must be tightly controlled not only to guarantee efficient protection from invading pathogens and oncogenic cells but also to avoid exaggerated immune responses and autoimmunity. This is achieved through interactions amongst leukocytes themselves, by signals from stromal cells and also by various hormones, including glucocorticoids. The glucocorticoids are a class of steroid hormones that exert a wide range of anti-inflammatory and immunosuppressive activities after binding to the glucocorticoid receptor. The power of these hormones was acknowledged many decades ago, and today synthetic derivatives are widely used in the treatment of inflammatory disorders, autoimmunity and cancer. In this review, we summarize our present knowledge of the molecular mechanisms of glucocorticoid action, their influence on specific leukocytes and the induction of thymocyte apoptosis, with an emphasis on how molecular genetics has contributed to our growing, although still incomplete, understanding of these processes.

Honokiol overcomes conventional drug resistance in human multiple myeloma by induction of caspase-dependent and -independent apoptosis

Honokiol (HNK) is an active component purified from magnolia, a plant used in traditional Chinese and Japanese medicine. Here we show that HNK significantly induces cytotoxicity in human multiple myeloma (MM) cell lines and tumor cells from patients with relapsed refractory MM. Neither coculture with bone marrow stromal cells nor cytokines (interleukin-6 and insulin-like growth factor-1) protect against HNK-induced cytotoxicity. Although activation of caspases 3, 7, 8, and 9 is triggered by HNK, the pan-caspase inhibitor z-VAD-fmk does not abrogate HNK-induced apoptosis. Importantly, release of an executioner of caspase-independent apoptosis, apoptosis-inducing factor (AIF), from mitochondria is induced by HNK treatment. HNK induces apoptosis in the SU-DHL4 cell line, which has low levels of caspase 3 and 8 associated with resistance to both conventional and novel drugs. These results suggest that HNK induces apoptosis via both caspase-dependent and -independent pathways. Furthermore, HNK enhances MM cell cytotoxicity and apoptosis induced by bortezomib. In addition to its direct cytotoxicity to MM cells, HNK also represses tube formation by endothelial cells, suggesting that HNK inhibits neovascurization in the bone marrow microenvironment. Taken together, our results provide the preclinical rationale for clinical protocols of HNK to improve patient outcome in MM.

Increased peripheral platelet destruction and caspase-3–independent programmed cell death of bone marrow megakaryocytes in myelodysplastic patients

To investigate underlying mechanisms of thrombocytopenia in myelodysplastic syndrome (MDS), radiolabeled platelet studies were performed in 30 MDS patients with platelet counts less than 100 × 109/L. Furthermore, plasma thrombopoietin and glycocalicin index (a parameter of platelet or megakaryocyte destruction) were determined. Mean platelet life (MPL), corrected for the degree of thrombocytopenia, was reduced in 15 of 30 patients (4.3 ± 0.9 days [mean ± SD] vs 6.0 ± 1.3, P = .0003). Platelet production rate (PPR) was reduced in 25 of 30 patients (68 ± 34 × 109/d vs 220 ± 65, P < .0001). Thrombopoietin levels were not significantly correlated with the PPR. However, the glycocalicin index was significantly higher compared with controls (15 ± 16 vs 0.7 ± 0.2, P = .001) and significantly correlated with the PPR (P = .02, r = -0.5), but not with the MPL (P = 1.8). Ultrastructural studies demonstrated necrosis-like programmed cell death (PCD) in mature and immature megakaryocytes (n = 9). Immunohistochemistry of the bone marrow biopsies demonstrated no positive staining of MDS megakaryocytes for activated caspase-3 (n = 24) or cathepsin D (n = 21), while activated caspase-8 was demonstrated in a subgroup of patients (5/21) in less than 10% of megakaryocytes. These results indicate that the main cause of thrombocytopenia in MDS is caspase-3–independent necrosis-like PCD resulting in a decreased PPR in conjunction with an increased glycocalicin index.

Comparative study of apoptosis-related gene loci in human, mouse and rat genomes

Many genes are involved in mammalian cell apoptosis pathway. These apoptosis genes often contain characteristic functional domains, and can be classified into at least 15 functional groups, according to previous reports. Using an integrated bioinformatics platform for motif or domain search from three public mammalian proteomes (International Protein Index database for human, mouse, and rat), we systematically cataloged all of the proteins involved in mammalian apoptosis pathway. By localizing those proteins onto the genomes, we obtained a gene locus centric apoptosis gene catalog for human, mouse and rat. Further phylogenetic analysis showed that most of the apoptosis related gene loci are conserved among these three mammals. Interestingly, about one-third of apoptosis gene loci form gene clusters on mammal chromosomes, and exist in the three species, which indicated that mammalian apoptosis gene orders are also conserved. In addition, some tandem duplicated gene loci were revealed by comparing gene loci clusters in the three species. All data produced in this work were stored in a relational database and may be viewed at http://pcas.cbi.pku.edu.cn/database/apd.php.

Death by design: apoptosis, necrosis and autophagy

Apoptosis is the principal mechanism by which cells are physiologically eliminated in metazoan organisms. During apoptotic death, cells are neatly carved up by caspases and packaged into apoptotic bodies as a mechanism to avoid immune activation. Recently, necrosis, once thought of as simply a passive, unorganized way to die, has emerged as an alternate form of programmed cell death whose activation might have important biological consequences, including the induction of an inflammatory response. Autophagy has also been suggested as a possible mechanism for non-apoptotic death despite evidence from many species that autophagy represents a survival strategy in times of stress. Recent advances have helped to define the function of and mechanism for programmed necrosis and the role of autophagy in cell survival and suicide.

Caspase-10 triggers Bid cleavage and caspase cascade activation in FasL-induced apoptosis

In contrast to caspase-8, controversy exists as to the ability of caspase-10 to mediate apoptosis in response to FasL. Herein, we have shown activation of caspase-10, -3, and -7 as well as B cell lymphoma-2-interacting domain (Bid) cleavage and cytochrome c release in caspase-8-deficient Jurkat (I9-2) cells treated with FasL. Apoptosis was clearly induced as illustrated by nuclear and DNA fragmentation. These events were inhibited by benzyloxycarbonyl-VAD-fluoromethyl ketone, a broad spectrum caspase inhibitor, indicating that caspases were functionally and actively involved. Benzyloxycarbonyl-AEVD-fluoromethyl ketone, a caspase-10 inhibitor, had a comparable effect. FasL-induced cell death was not completely abolished by caspase inhibitors in agreement with the existence of a cytotoxic caspase-independent pathway. In subpopulations of I9-2 cells displaying distinct caspase-10 expression levels, cell sensitivity to FasL correlated with caspase-10 expression. A robust caspase activation, Bid cleavage, and DNA fragmentation were observed in cells with high caspase-10 levels but not in those with low levels. In vitro, caspase-10, as well as caspase-8, could cleave Bid to generate active truncated Bid (p15). Altogether, our data strongly suggest that caspase-10 can serve as an initiator caspase in Fas signaling leading to Bid processing, caspase cascade activation, and apoptosis.

Sensitization of stefin B-deficient thymocytes towards staurosporin-induced apoptosis is independent of cysteine cathepsins

Stefin B (cystatin B) is an inhibitor of lysosomal cysteine cathepsins and does not inhibit cathepsin D, E (aspartic) or cathepsin G (serine) proteinases. In this study, we have investigated apoptosis triggered by camptothecin, staurosporin (STS), and anti-CD95 monoclonal antibody in the thymocytes from the stefin B-deficient mice and wild-type mice. We have observed increased sensibility to STS-induced apoptosis in the thymocytes of stefin B-deficient mice. Pretreatment of cells with pan-caspase inhibitor z-Val-Ala-Asp(OMe)-fluoromethylketone completely inhibited phosphatidylserine externalization and caspase activation, while treatment with inhibitor of calpains- and papain-like cathepsins (2S,3S)-trans-epoxysuccinyl-leucylamido-3-methyl-butane ethyl ester did not prevent caspase activation nor phosphatidylserine exposure. We conclude that sensitization to apoptosis induced by STS in thymocytes of stefin B-deficient and wild-type mice is not dependent on cathepsin inhibition by stefin B.

The P2X7 receptor is a candidate product of murine and human lupus susceptibility loci: a hypothesis and comparison of murine allelic products

Systemic lupus erythematosus and its murine equivalent, modelled in the New Zealand Black and New Zealand White (NZB × NZW)F₁ hybrid strain, are polygenic inflammatory diseases, probably reflecting an autoimmune response to debris from cells undergoing programmed cell death. Several human and murine loci contributing to disease have been defined. The present study asks whether the proinflammatory purinergic receptor P2X₇, an initiator of a form of programmed cell death known as aponecrosis, is a candidate product of murine and human lupus susceptibility loci. One such locus in (NZB × NZW)F₁ mice is lbw3, which is situated at the distal end of NZW chromosome 5. We first assess whether NZB mice and NZW mice carry distinct alleles of the P2RX₇ gene as expressed by common laboratory strains, which differ in sensitivity to ATP stimulation. We then compare the responses of NZB lymphocytes, NZW lymphocytes and (NZB × NZW)F₁ lymphocytes to P2X₇ stimulation. NZB and NZW parental strains express the distinct P2X₇-L and P2X₇-P alleles of P2RX₇, respectively, while lymphocytes from these and (NZB × NZW)F₁ mice differ markedly in their responses to P2X₇ receptor stimulation. NZB mice and NZW mice express functionally distinct alleles of the proinflammatory receptor, P2X₇. We show that current mapping suggests that murine and human P2RX₇ receptor genes lie within lupus susceptibility loci lbw3 and SLEB4, and we argue that these encode a product with the functional characteristics consistent with a role in lupus. Furthermore, we argue that aponecrosis as induced by P2X₇ is a cell death mechanism with characteristics that potentially have particular relevance to disease pathogenesis.

Polysorbate 80 increases the susceptibility to oxidative stress in rat thymocytes

Effect of simultaneous application of polysorbate 80, a nonionic surfactant widely used in pharmaceutical products, and hydrogen peroxide on rat thymocytes was examined to see if polysorbate 80 increases the susceptibility to oxidative stress because this surfactant decreases the cellular content of glutathione. Polysorbate 80 at clinically-relevant concentrations increases the cytotoxicity of hydrogen peroxide under the in vitro condition. Result suggests that polysorbate 80 may increase the susceptibility of cells to oxidative stress.

Ischemia leads to apoptosis--and necrosis-like neuron death in the ischemic rat hippocampus

Morphological evidence of apoptosis in transient forebrain ischemia is controversial. We therefore investigated the time sequence of apoptosis-related antigens by immunohistochemistry and correlated it with emerging nuclear patterns of cell death in a model of transient forebrain ischemia in CA1 pyramidal cells of the rat hippocampus. The earliest ischemic changes were found on day 2 and 3, reflected by an upregulation of phospho-c-Jun in a proportion of morphologically intact CA1 neurons, which matched the number of neurons that succumbed to ischemia at later time points. At day 3 and later 3 ischemic cell death morphologies became apparent: pyknosis, apoptosis-like cell death and necrosis-like cell death, which were confirmed by electron microscopy. Activated caspase-3 was present in the vast majority of cells with apoptosis-like morphology as well as in a small subset of cells undergoing necrosis; its expression peaked on days 3 to 4. Silver staining for nucleoli, which are a substrate for caspase-3, revealed a profound loss of nucleoli in cells with apoptosis-like morphology, whereas cells with necrosis-like morphology showed intact nucleoli. Overall, cells with apoptosis-like morphology and/or caspase-3 expression represented a minor fraction (<10%) of ischemic neurons, while the vast majority followed a necrosis-like pathway. Our studies suggest that CA1 pyramidal cell death following transient forebrain ischemia may be initiated through c-Jun N-terminal kinase (JNK) pathway activation, which then either follows an apoptosis-like cell death pathway or leads to secondary necrosis.

Multiple cell death programs: Charon's lifts to Hades

Cells use different pathways for active self-destruction as reflected by different morphology: while in apoptosis (or "type I") nuclear fragmentation associated with cytoplasmic condensation but preservation of organelles is predominant, autophagic degradation of cytoplasmic structures preceding nuclear collapse is a characteristic of a second type of programmed cell death (PCD). The diverse morphologies can be attributed--at least to some extent--to distinct biochemical and molecular events (e.g. caspase-dependent and -independent death programs; DAP-kinase activity, Ras-expression). However, apoptosis and autophagic PCD are not mutually exclusive phenomena. Rather, diverse PCD programs emerged during evolution, the conservation of which apparently allows cells a flexible response to environmental changes, either physiological or pathological.

Chlamydia pneumoniae induces aponecrosis in human aortic smooth muscle cells

Background

The intracellular bacterium Chlamydia pneumoniae is suspected to play a role in formation and progression of atherosclerosis. Many studies investigated cell death initiation versus inhibition by Chlamydia pneumoniae in established cell lines but nothing is known in primary human aortic smooth muscle cells, a cell type among others known to be involved in the formation of the atherosclerotic plaque. Type of cell death was analyzed by various methods in primary aortic smooth muscle cells after infection with Chlamydia pneumoniae to investigate a possible pathogenic link in atherosclerosis.

Results

Chlamydiae were found to be localized up to 72 h post infection in aortic smooth muscle cells either as single bacteria or inside of large inclusions. Quantification of host cell death by lactate dehydrogenase release assay revealed strictly dose and time dependent lysis for all tested isolates of Chlamydia pneumoniae. Phosphatidylserine exposure was detected by flow cytometry in Chlamydia pneumoniae infected cells. Ultrastructure of Chlamydia pneumoniae infected human aortic smooth muscle cells showed extensive membrane- and organelle damage, chromatin condensation but no nuclear fragmentation. DNA fragmentation as well as cell membrane permeability was analyzed by TUNEL and NHS-biotin staining and occurred exclusively in cells carrying Chlamydia pneumoniae spots but not in smooth muscle cells with inclusions. These morphological features of cell death were not accompanied by an activation of caspase-3 as revealed by analysis of enzyme activity but involved mitochondrial membrane depolarization as shown by TMRE uptake and release of cytochrome c from mitochondria.

Conclusion

This study provides evidence that Chlamydia pneumoniae induce a spot like infection in human aortic smooth muscle cells, which results in a chimeric cell death with both apoptotic and necrotic characteristics. This aponecrotic cell death may assist chronic inflammation in atherosclerotic blood vessels.

"The stress of dying": the role of heat shock proteins in the regulation of apoptosis

Heat shock proteins (Hsps) are a family of highly homologous chaperone proteins that are induced in response to environmental, physical and chemical stresses and that limit the consequences of damage and facilitate cellular recovery. The underlying ability of Hsps to maintain cell survival correlates with an inhibition of caspase activation and apoptosis that can, but does not always, depend upon their chaperoning activities. Several mechanisms proposed to account for these observations impact on both the "intrinsic", mitochondria-dependent and the "extrinsic", death-receptor-mediated pathways to apoptosis. Hsps can inhibit the activity of pro-apoptotic Bcl-2 proteins to prevent permeabilization of the outer mitochondrial membrane and release of apoptogenic factors. The disruption of apoptosome formation represents another mechanism by which Hsps can prevent caspase activation and induction of apoptosis. Several signaling cascades involved in the regulation of key elements within the apoptotic cascade are also subject to modulation by Hsps, including those involving JNK, NF-kappaB and AKT. The coordinated activities of the Hsps thus modulate multiple events within apoptotic pathways to help sustain cell survival following damaging stimuli.

The role of tumour necrosis factor (TNF-alpha) in experimental autoimmune uveoretinitis (EAU)

The pleiotropic cytokine tumour necrosis factor-alpha (TNF-alpha) is released from cells that include macrophages and T-cells during inflammatory responses, orchestrating the initiation of further leucocytic infiltration via adhesion molecule upregulation, dendritic cell maturation and survival, macrophage activation and driving Th1 T-cells responses within tissues. Exposure to TNF also plays a role in maintaining tissue homeostasis, particularly relating to resident cell responses of both microglia and retinal pigment epithelium. Depending on the balance between duration and dose of TNF exposure, an environment where full expression of inflammatory and autoimmune responses within tissues may occur. In experimental autoimmune uveoretinitis (EAU), increased tissue concentrations of TNF facilitate the on-going T-cell effector responses and macrophage activation. These are responsible for targeted and bystander tissue damage and can be suppressed by anti-TNF therapies, in particular, those directed at the p55 TNF receptor. The ability to suppress disease experimentally has led to the successful translation of anti-TNF therapy for treatment of uveitis in cohort studies and phase I/II trials where, additionally, altered peripheral blood CD4(+) T-cell profiles can be demonstrated following each treatment.

Rescuing melanoma epitope-specific cytolytic T lymphocytes from activation-induced cell death, by SP600125, an inhibitor of JNK: implications in cancer immunotherapy

Activation-induced cell death (AICD) as well as programmed cell death (PCD) serve to control the expansion of activated T cells to limit untoward side effects of continued effector responses by T cells and to maintain homeostasis. AICD of T cells in tumor immunotherapy can be counterproductive particularly if the activated T cells undergo apoptotic death after the very first secondary encounter of the specific epitope. We examined the extent to which tumor epitope-specific CTLs that are activated and expanded in an in vitro-matured dendritic cell-based primary stimulation protocol undergo AICD following their first secondary encounter of the cognate epitope. Using the MART-1(27-35) epitope as a prototype vaccine epitope, we also examined whether these CTLs could be rescued from AICD. Our results demonstrate that a substantial fraction of MART-1(27-35) epitope-specific primary CTLs undergo AICD upon the very first secondary encounter of the cognate epitope. The AICD in these CTLs is neither caspase dependent nor is it triggered by the extrinsic death signaling pathways (Fas, TNFR, etc.). These CTLs, interestingly, could be rescued from AICD by the JNK inhibitor, SP600125. We also found that SP600125 interferes with their IFN-gamma response but does not block their cytolytic function. The rescued CTLs, however, regain their capacity to synthesize IFN-gamma if continued in culture without the inhibitor. These observations have implications in tumor immunotherapy and in further studies for regulation of AICD in CTLs.

Membrane lipids and cell death: an overview

In this article we overview major aspects of membrane lipids in the complex area of cell death, comprising apoptosis and various forms of programmed cell death. We have focused here on glycerophospholipids, the major components of cellular membranes. In particular, we present a detailed appraisal of mitochondrial lipids that attract increasing interest in the field of cell death, while the knowledge of their re-modelling and traffic remains limited. It is hoped that this review will stimulate further studies by lipid experts to fully elucidate various aspects of membrane lipid homeostasis that are discussed here. These studies will undoubtedly reveal new and important connections with the established players of cell death and their action in promoting or blocking membrane alteration of mitochondria and other organelles. We conclude that the new dynamic era of cell death research will pave the way for a better understanding of the 'chemistry of apoptosis'.

Preapoptotic Chromatin Condensation Upstream of the Mitochondrial Checkpoint

When added for a short period (2-4 h) to cells, the kinase inhibitor staurosporine (STS), can trigger double strand breaks, the formation of nuclear foci containing phosphorylated H2AX, Chk2, and p53, a decrease in transcription, and a minor degree of peripheral chromatin condensation. This "preapoptotic chromatin condensation" (PACC) occurs before mitochondrial membrane permeabilization (MMP) and caspase activation become detectable and is not inhibited by Z-VAD-fmk or Bcl-2. PACC is followed by classical apoptosis, when cells are cultured overnight, even when STS is removed from the system. After overnight incubation, STS-pretreated cells manifest mitochondrial cytochrome c release, caspase activation, phosphatidylserine exposure, and apoptotic DNA fragmentation. Caspase or MMP inhibitors did not influence the advent of PACC yet did suppress the evolution of PACC toward apoptosis. Importantly, two unrelated MMP inhibitors (viral mitochondrial inhibitor of apoptosis (vMIA) from cytomegalovirus and mitochondrion-targeted Bcl-2) had a larger range of effects than the pan-caspase inhibitor Z-VAD-fmk. Caspase inhibition simply prevented the transition from PACC to apoptosis yet did not reverse PACC and did not restore transcription. In contrast, Bcl-2 and vMIA allowed for the repair of the DNA lesions, correlating with the reestablishment of active transcription. PACC could also be induced by a gross perturbation of RNA synthesis or primary DNA damage. Again, inhibition of MMP (but not that of caspases) reversed PACC induced by these stimuli. In synthesis, our data reveal the unexpected capacity of STS to induce DNA lesions and suggest qualitative differences in the cytoprotective and DNA repair-inducing potential of different apoptosis inhibitors.

The Contraction Phase of Virus-Specific CD8+T Cells Is Unaffected by a Pan-Caspase Inhibitor

The effectiveness of protection conferred by CD8(+) memory T cells is determined by both their quality and their quantity, which suggests that vaccine efficacy might be improved if it were possible to increase the size of the memory pool. Approximately 90% of virus-specific CD8(+) T cells die during the contraction phase and, herein, we have attempted to increase the memory pool by reducing CD8(+) T cell death. CD8(+) T cell contraction has been attributed to apoptosis, or programmed cell death (PCD), which, classically, is dependent on caspases. Caspase-dependent PCD can be prevented by the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp (OMe)-fluoromethylketone (zVAD), and here we evaluate the effect of this compound on virus-specific T cell responses in mice. zVAD prevented caspase-dependent PCD of freshly isolated virus-specific T cells in tissue culture, and a fluorescent analog, FITC-VAD, entered CD8(+) T cells following in vivo injection. However, despite using 11 different regimens of zVAD administration in vivo, no significant effects on CD8(+) or CD4(+) memory T cell numbers were observed. Furthermore, the CD8(+) memory T cell responses to secondary virus infection were indistinguishable, both qualitatively and quantitatively, in zVAD-treated and normal mice. The absence of effect cannot be attributed to a technical flaw, because identical doses of zVAD were able to rescue mice from hepatocyte apoptosis and lethal intrahepatic hemorrhage, induced by inoculation of anti-Fas Ab. We conclude that the contraction phase of the virus-specific T cell response is unlikely to require caspase-dependent PCD. We propose that contraction can be mediated by an alternative, caspase-independent pathway(s).

Cell death pathways in pancreatitis and pancreatic cancer

The understanding of the regulation of apoptosis and necrosis, the two principal cell death pathways, is becoming exceedingly important in investigations of the pathogenesis and treatment of pancreatitis and pancreatic cancer. For example, in acute pancreatitis significant amounts of pancreatic necrosis are associated with increased morbidity and mortality. Thus, determining the key steps regulating necrosis should provide insights into potential therapeutic strategies for improving outcome in these patients. On the other hand, in pancreatic cancer various survival mechanisms act to prevent cell death, resulting in promotion of tumor growth and metastasis. Resistance of pancreatic cancer to apoptosis is the key factor preventing responses to therapies. Investigations of the regulation of cell death mechanisms specific to pancreatic cancer should lead to improvements in our current therapies for this disease. The present review is designed to provide information about cell death pathways in pancreatitis and pancreatic cancer with reference to areas that need further investigation, as well as to provide measurement techniques adapted to pancreatic tissue and cells.

Mitochondrial dysfunction is a primary event in renal cell oxalate toxicity

BACKGROUND

In cultured renal epithelial cells, exposure to oxalate, a constituent of many kidney stones, elicits a cascade of responses that often leads to cell death. Oxalate toxicity is mediated via generation of reactive oxygen species (ROS) in a process that depends at least in part upon lipid signaling molecules that are generated through membrane events that culminate in phospholipase A2 (PLA2) activation. The present studies asked whether mitochondria, a major site of ROS production, were targets of oxalate toxicity, and if so, whether mitochondrial responses to oxalate were mediated by PLA2 activation.

METHODS

Effects of oxalate and various lipids on mitochondrial membrane potential (DeltaPsim) were measured in Madin-Darby canine kidney (MDCK) cell monolayers using 5,5',6,6'-tetrachloro 1,1',3,3'-tetraethylbenzimidazolylcarbocyanine iodide (JC-1), a DeltaPsim-sensitive dye. Other studies assayed caspases, serine proteases activated during apoptosis, in response to oxalate or lipid signaling molecules. Additional studies asked whether oxalate or lipids produced by PLA2 activation promoted ROS formation in isolated renal mitochondria.

RESULTS

Oxalate exposure decreased MDCK cell DeltaPsim within 30 minutes, a response attenuated by arachidonyl trifluoromethyl ketone (AACOCF3), an inhibitor of cytosolic PLA2 (cPLA2). Exposure to arachidonic acid or to lysophosphatidylcholine (lyso-PC), lipid products of PLA2 activation, or to ceramide, another lipid signal generated in MDCK cells following oxalate exposure, also depolarized MDCK cell DeltaPsim and increased the number of caspase-positive cells. Isolated renal mitochondria responded to oxalate, arachidonic acid, lyso-PC, and ceramide by increasing their accumulation of ROS, lipid peroxides, and oxidized thiol proteins.

CONCLUSION

These studies suggest that lipid signaling molecules released after oxalate-induced PLA2 activation trigger marked, rapid changes in mitochondrial function that may mediate toxicity in renal epithelial cells.