Caspase activation involves the formation of the aposome, a large (approximately 700 kDa) caspase-activating complex

Daphnoretin induces cell cycle arrest and apoptosis in human osteosarcoma (HOS) cells

In this study antiproliferation, cell cycle arrest and apoptosis induced by daphnoretin in human osteosarcoma (HOS) cells were investigated. Antiproliferative activity was measured with the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. The IC(50) value of daphnoretin was 3.89 μM after 72 h treatment. Induction of apoptosis was evidenced by apoptotic body appearance and Annexin V-FITC/PI apoptosis detection kit. Flow cytometric analysis indicated daphnoretin arrested the cell cycle in the G2/M phase. Western-blot assay showed that the G2/M phase arrest was accompanied by down-regulation of cdc2, cyclin A and cyclin B1. Moreover, daphnoretin inhibited Bcl-2 expression and induced Bax expression to desintegrate the outer mitochondrial membrane and causing cytochrome c release. Mitochondrial cytochrome c release was associated with the activation of caspase-9 and caspase-3 cascade. Our results demonstrated that daphnoretin caused death of HOS cells by blocking cells successively in G2/M phases and activating the caspase-3 pathway.

Inhibition of caspase-9 by stabilized peptides targeting the dimerization interface

Caspases comprise a family of dimeric cysteine proteases that control apoptotic programmed cell death and are therefore critical in both organismal development and disease. Specific inhibition of individual caspases has been repeatedly attempted, but has not yet been attained. Caspase-9 is an upstream or initiator caspase that is regulated differently from all other caspases, as interaction with natural inhibitor X-linked inhibitor of apoptosis protein (XIAP)-baculovirus inhibitory repeat 3 (BIR3) occurs at the dimer interface maintaining caspase-9 in an inactive monomeric state. One route to caspase-9-specific inhibition is to mimic this interaction, which has been localized to the α5 helix of XIAP-BIR3. We have developed three types of stabilized peptides derived from the α5 helix, using incorporation of aminoisobutyric acid, the avian pancreatic polypeptide (aPP)-scaffold or aliphatic staples. The stabilized peptides are helical in solution and achieve up to 32 μM inhibition, indicating that this allosteric site at the caspase-9 dimerization interface is regulatable with low-molecular weight synthetic ligands and is thus a druggable site. The most potent peptides against caspase-9 activity are the aPP-scaffolded peptides. Other caspases, which are not regulated by dimerization, should not be inactivated by these peptides. Given that all of the peptides attain helical structures but cannot recapitulate the high-affinity inhibition of the intact BIR3 domain, it has become clear that interactions of caspase-9 with the BIR3 exosite are essential for high-affinity binding. These results explain why the full XIAP-BIR3 domain is required for maximal inhibition and suggest a path forward for achieving allosteric inhibition at the dimerization interface using peptides or small molecules.

Identification of a conserved anti-apoptotic protein that modulates the mitochondrial apoptosis pathway

Here we identified an evolutionarily highly conserved and ubiquitously expressed protein (C9orf82) that shows structural similarities to the death effector domain of apoptosis-related proteins. RNAi knockdown of C9orf82 induced apoptosis in A-549 and MCF7/casp3-10b lung and breast carcinoma cells, respectively, but not in cells lacking caspase-3, caspase-10 or both. Apoptosis was associated with activated caspases-3, -8, -9 and -10, and inactivation of caspases 10 or 3 was sufficient to block apoptosis in this pathway. Apoptosis upon knockdown of C9orf82 was associated with increased caspase-10 expression and activation, which was required for the generation of an 11 kDa tBid fragment and activation of Caspase-9. These data suggest that C9orf82 functions as an anti-apoptotic protein that modulates a caspase-10 dependent mitochondrial caspase-3/9 feedback amplification loop. We designate this ubiquitously expressed and evolutionarily conserved anti-apoptotic protein Conserved Anti-Apoptotic Protein (CAAP). We also demonstrated that treatment of MCF7/casp3-10b cells with staurosporine and etoposides induced apoptosis and knockdown of CAAP expression. This implies that the CAAP protein could be a target for chemotherapeutic agents.

cIAPs block Ripoptosome formation, a RIP1/caspase-8 containing intracellular cell death complex differentially regulated by cFLIP isoforms

The intracellular regulation of cell death pathways by cIAPs has been enigmatic. Here we show that loss of cIAPs promotes the spontaneous formation of an intracellular platform that activates either apoptosis or necroptosis. This 2 MDa intracellular complex that we designate “Ripoptosome” is necessary but not sufficient for cell death. It contains RIP1, FADD, caspase-8, caspase-10, and caspase inhibitor cFLIP isoforms. cFLIP_L prevents Ripoptosome formation, whereas, intriguingly, cFLIP_S promotes Ripoptosome assembly. When cIAPs are absent, caspase activity is the “rheostat” that is controlled by cFLIP isoforms in the Ripoptosome and decides if cell death occurs by RIP3-dependent necroptosis or caspase-dependent apoptosis. RIP1 is the core component of the complex. As exemplified by our studies for TLR3 activation, our data argue that the Ripoptosome critically influences the outcome of membrane-bound receptor triggering. The differential quality of cell death mediated by the Ripoptosome may cause important pathophysiological consequences during inflammatory responses.

Treatment of ovarian cancer cells with nutlin-3 and resveratrol combination leads to apoptosis via caspase activation

The current study was focused on the induction of apoptotic effects of resveratrol along with the combination treatments of nutlin-3 and transforming growth factor-β (TGF-β) against the human ovarian cancer cell line A2780/CP70. To determine the extent of apoptosis following the above-mentioned treatments, we assessed the execution of apoptotic events that proceed via caspase activation and cytochrome c release. We estimated the caspase-3 and -9 activities using a direct enzymatic assay that measures the cleavage of synthetic peptide substrate (N-acetyl-Asp-Glu-Val-Asp-p-nitroanilide). Our experiments showed an increase in caspase-3 and -9 activities in the cells that were treated with the combination of resveratrol (5 μM) with nutlin-3 (5 μM) or TGF-β (1 μg/mL). Since activation of procaspase-3 by caspase-9 requires the release of cytochrome c into the cytoplasm, we measured the levels of cytochrome c in the cytoplasm by western blot experiments. The data indicated a considerable increase in caspase-3 and cytochrome c levels when cells were treated with drugs for 24 hours. Experiments with 4,6'-diamino-2-phenylindole dihydrochloride (DAPI) staining also confirmed the induction of apoptosis in all the above-mentioned treatments done at 24 and 48 hours. These results support our hypothesis that resveratrol combination can induce programmed cell death at doses that are less than half of what is typically needed for nutlin-3 and TGF-β to induce apoptosis.

Lack of muscle recovery after immobilization in old rats does not result from a defect in normalization of the ubiquitin-proteasome and the caspase-dependent apoptotic pathways

Immobilization periods increase with age because of decreased mobility and/or because of increased pathological episodes that require bed-rest. Then, sarcopaenia might be partially explained by an impaired recovery of skeletal muscle mass after a catabolic state due to an imbalance of muscle protein metabolism, apoptosis and cellular regeneration. Mechanisms involved during muscle recovery have been little studied and in elderly they remain almost unknown. We show, in rats, that a short immobilization period during ageing initiated muscle atrophy that was indeed not recovered after 40 days. Immobilization was associated with an activation of both the ubiquitin-proteasome and the mitochondria-associated apoptotic pathways and the inflammatory and redox processes, and a decrease of cellular regeneration. We show that the lack of muscle recovery during ageing is not due to a defect in proteolysis or apoptosis down-regulation. These observations lead us to hypothesize that muscle protein synthesis activation after immobilization was altered during ageing.

Naofen, a novel WD40-repeat protein, mediates spontaneous and tumor necrosis factor-induced apoptosis

Naofen has recently been identified from the rat brain/spinal cord cDNA library as a substance reactive against an anti-shigatoxin (Stx)-2 antibody. Naofen mRNA is composed of 4620 nucleotides and encodes 1170 amino acids. Naofen contains four WD-repeat domains in its N-terminus and is ubiquitously distributed in many tissues of the rat. Tumor necrosis factor (TNF)-alpha enhanced the expression of naofen mRNA in HEK293 cells in a dose-dependent manner. Furthermore, naofen siRNA, which predominantly knocked down the expression of naofen mRNA, significantly reduced both TNF-alpha-induced caspase-3 activation and apoptosis in HEK293 cells. Overexpression of naofen in HEK293 cells (FLAG-NF) spontaneously induced caspase -3 activation and apoptosis, and showed extremely high susceptibility to TNF-alpha-induced apoptosis. These results indicated that naofen may function as a novel modulator activating caspase-3, and promoting TNF-alpha-stimulated apoptosis.

Cell death pathways--potential therapeutic targets

Programmed cell death and its morphological manifestation termed apoptosis is a conserved pathway that appears to operate in all multicellular organisms. During embryonic development, cell death is essential for successful organogenesis, and apoptosis also operates in adult organisms to maintain normal cellular homeostasis. The removal of disordered cells by a controlled cellular mechanism is especially critical in long-lived mammals that must integrate multiple physiological as well as pathological death signals. Gain- and loss-of-function models of genes in the core apoptotic pathway suggest that perturbation of cellular homeostasis can be a primary pathogenic event that results in disease. Indeed, there is now compelling evidence that insufficient apoptosis can manifest as cancer or autoimmunity, whereas accelerated cell death is evident in acute and chronic degenerative diseases, further highlighting the fact that deregulation of cell death pathways has major health implications. Not surprisingly, during the past 25 years a huge endeavour aimed at unravelling this fundamental biological process has led to major advances in our understanding of cell death pathways. Therapeutic strategies to manipulate apoptosis have immense potential and this review highlights several potentially viable drug targets for modulating cell death that have been discovered from the elegant work of many scientists in elucidating the protein components and key regulators of apoptosis signalling pathways.

SPERM CASPASES BECOME MORE ACTIVATED IN INFERTILITY PATIENTS THAN IN HEALTHY DONORS DURING CRYOPRESERVATION

The programmed cell death (PCD, the apoptosis) is associated with the activation of the "death enzymes" caspases and very likely plays a role in the decrease of sperm vitality during cryopreservation. The activation of pan-caspases was examined in fresh and cryostored sperm by fluorescence microscopy applying a cell permeable and noncytotoxic carboxy-fluorescein labelled caspase inhibitor. Cryopreservation increased significantly the percentage of spermatozoa with activated pan-caspases (aCP) from 21 +/- 2.6 to 47 +/- 5.8 % (mean +/- SEM). Quantitative Western blot analyses confirmed the activation of caspase-1, -8, and -9 in detail on protein level after cryopreservation, whereas, the caspases of sperm of infertility patients showed a higher activation status than donors' sperm. This effect raised with increasing glycerol concentration from 7-14 %. The higher level in activation of caspases in cryostored spermatozoa of infertility patients may indicate that these cells have a lower cryotolerance and a higher susceptibility to caspase activation than does the sperm of donors.

The Apaf-1*procaspase-9 apoptosome complex functions as a proteolytic-based molecular timer

During stress-induced apoptosis, the initiator caspase-9 is activated by the Apaf-1 apoptosome and must remain bound to retain significant catalytic activity. Nevertheless, in apoptotic cells the vast majority of processed caspase-9 is paradoxically observed outside the complex. We show herein that apoptosome-mediated cleavage of procaspase-9 occurs exclusively through a CARD-displacement mechanism, so that unlike the effector procaspase-3, procaspase-9 cannot be processed by the apoptosome as a typical substrate. Indeed, procaspase-9 possessed higher affinity for the apoptosome and could displace the processed caspase-9 from the complex, thereby facilitating a continuous cycle of procaspase-9 recruitment/activation, processing, and release from the complex. Owing to its rapid autocatalytic cleavage, however, procaspase-9 per se contributed little to the activation of procaspase-3. Thus, the Apaf-1 apoptosome functions as a proteolytic-based 'molecular timer', wherein the intracellular concentration of procaspase-9 sets the overall duration of the timer, procaspase-9 autoprocessing activates the timer, and the rate at which the processed caspase-9 dissociates from the complex (and thus loses its capacity to activate procaspase-3) dictates how fast the timer 'ticks' over.

Targeting autophagy potentiates tyrosine kinase inhibitor-induced cell death in Philadelphia chromosome-positive cells, including primary CML stem cells

Imatinib mesylate (IM), a potent inhibitor of the BCR/ABL tyrosine kinase, has become standard first-line therapy for patients with chronic myeloid leukemia (CML), but the frequency of resistance increases in advancing stages of disease. Elimination of BCR/ABL-dependent intracellular signals triggers apoptosis, but it is unclear whether this activates additional cell survival and/or death pathways. We have shown here that IM induces autophagy in CML blast crisis cell lines, CML primary cells, and p210BCR/ABL-expressing myeloid precursor cells. IM-induced autophagy did not involve c-Abl or Bcl-2 activity but was associated with ER stress and was suppressed by depletion of intracellular Ca2+, suggesting it is mechanistically nonoverlapping with IM-induced apoptosis. We further demonstrated that suppression of autophagy using either pharmacological inhibitors or RNA interference of essential autophagy genes enhanced cell death induced by IM in cell lines and primary CML cells. Critically, the combination of a tyrosine kinase inhibitor (TKI), i.e., IM, nilotinib, or dasatinib, with inhibitors of autophagy resulted in near complete elimination of phenotypically and functionally defined CML stem cells. Together, these findings suggest that autophagy inhibitors may enhance the therapeutic effects of TKIs in the treatment of CML.

Mismatch repair protein deficiency compromises cisplatin-induced apoptotic signaling

Mismatch repair (MMR) proteins participate in cytotoxicity induced by certain DNA damage-inducing agents, including cisplatin (cis-diamminedichloroplatinum(II), CDDP), a cancer chemotherapeutic drug utilized clinically to treat a variety of malignancies. MMR proteins have been demonstrated to bind to CDDP-DNA adducts and initiate MMR protein-dependent cell death in cells treated with CDDP; however, the molecular events underlying this death remain unclear. As MMR proteins have been suggested to be important in clinical responses to CDDP, a clear understanding of MMR protein-dependent, CDDP-induced cell death is critical. In this report, we demonstrate MMR protein-dependent relocalization of cytochrome c to the cytoplasm and cleavage of caspase-9, caspase-3, and poly(ADP-ribose) polymerase upon treatment of cells with CDDP. Chemical inhibition of caspases specifically attenuates CDDP/MMR protein-dependent cytotoxicity, suggesting that a caspase-dependent signaling mechanism is required for the execution of this cell death. p53 protein levels were up-regulated independently of MMR protein status, suggesting that p53 is not a mediator of MMR-dependent, CDDP-induced death. This work is the first indication of a required signaling mechanism in CDDP-induced, MMR protein-dependent cytotoxicity, which can be uncoupled from other CDDP response pathways, and defines a critical contribution of MMR proteins to the control of cell death.

Activation of the caspase cascade underlies the rat trigeminal primary neuronal apoptosis induced by neonatal capsaicin administration

The systemic administration of capsaicin is known to cause a massive loss of sensory primary neurons in newborn rats. Here we examined the trigeminal ganglion neurons immunohistochemically for the possible induction of activated forms of caspases-9 and -3 following a subcutaneous injection of capsaicin in newborn rats. The DNA fragmentation signal was labeled by a TUNEL method. TUNEL-positive neurons were rare (< 0.5%) at 24 h after injection of the vehicle without capsaicin. After the capsaicin injection, TUNEL-positive neurons began to increase by 12 h, reached a peak at 24 h (11.4%), and returned to the control level by 120 h. Vehicle control levels of caspase- 9-immunoreactive (ir) and caspase-3-ir neurons were low (< 0.5%). Neonatal capsaicin administration induced caspase-9-immunoreactivity (ir) and -3-ir. The temporal distributions of caspase-9-ir and caspase-3-ir neurons were similar to those of TUNEL-positive neurons with peak expressions at 24 h of 13.2 and 11.1%, respectively. A double-stain analysis at 24 h post-injection indicated 72% of TUNEL-positive neurons were caspase-9-ir, and 70% caspase-3-ir. Conversely, 78 and 68% of caspase-9-ir and caspase-3-ir neurons, respectively, were TUNEL-positive. Comparison of two adjacent sections immunostained for the two different antigens revealed the co-expression of the two caspases. These results suggest that neonatal capsaicin triggers the caspase cascade and, thereby, induces trigeminal primary neuronal apoptosis.

Apoptosome assembly

Apoptosome refers to the multimeric protein complex that mediates activation of an initiator caspase at the onset of apoptosis. This chapter describes the assembly of three related apoptosomes from mammals, fruit flies, and worms. The assembly of the mammalian apoptosome, which is responsible for the activation of caspase-9, involves Apaf-1 and requires cytochrome c and ATP/dATP binding. Assembly of the apoptosome in Drosophila melanogaster, which activates caspase-9 homologue Dronc, involves the Apaf-1 homologue known as Dark/Hac-1/Dapaf-1. In Caenorhabditis elegans, assembly of the CED-4 apoptosome requires EGL-1-mediated dissociation of CED-9 (a Bcl-2 homologue) from the CED-4-CED-9 complex and subsequent oligomerization of CED-4. Recent biochemical and structural investigation revealed insights into the assembly and function of the various apoptosomes.

Phenethyl isothiocyanate induced apoptosis via down regulation of Bcl-2/XIAP and triggering of the mitochondrial pathway in MCF-7 cells

Although isothiocyanates have been shown to inhibit carcinogen-induced tumorigenesis, no studies have been made to determine their therapeutic potential for the treatment of breast cancer. In the present study, we evaluated the apoptotic activities of phenethyl isothiocyanate (PEITC) in human breast cancer MCF-7 cells. Exposure to PEITC potently reduced cell viability. In addition, DNA fragments and TUNEL positive nuclei were detected in PEITC-treated cells. Furthermore, PEITC induced apoptosis via activation of caspases 7 and 9 and the cleavage of PARP, and these effects were reversed by treatment with the caspase inhibitor, Z-VAD-fmk. PEITC also caused a decrease in the levels of Bcl-2 with a concomitant increase in Bax levels, which resulted in the release of cytochrome c. XIAP suppression and Smac translocation also contributed to the PEITC-induced apoptosis. However, PEITC did not increase the expressions of p53 and p21. Taken together, the results of this study demonstrate that PEITC significantly induces apoptosis via a mitochondrial pathway. Specifically, PEITC induced a change in the Bax/Bcl-2 ratios, XIAP levels and Smac translocation that was conjunction with the release of cytochrome c and following caspase activation. Therefore, PEITC has the potential for use as a therapeutic agent for the treatment of breast cancer.

Construction and analysis of a modular model of caspase activation in apoptosis

Background

A key physiological mechanism employed by multicellular organisms is apoptosis, or programmed cell death. Apoptosis is triggered by the activation of caspases in response to both extracellular (extrinsic) and intracellular (intrinsic) signals. The extrinsic and intrinsic pathways are characterized by the formation of the death-inducing signaling complex (DISC) and the apoptosome, respectively; both the DISC and the apoptosome are oligomers with complex formation dynamics. Additionally, the extrinsic and intrinsic pathways are coupled through the mitochondrial apoptosis-induced channel via the Bcl-2 family of proteins.

Results

A model of caspase activation is constructed and analyzed. The apoptosis signaling network is simplified through modularization methodologies and equilibrium abstractions for three functional modules. The mathematical model is composed of a system of ordinary differential equations which is numerically solved. Multiple linear regression analysis investigates the role of each module and reduced models are constructed to identify key contributions of the extrinsic and intrinsic pathways in triggering apoptosis for different cell lines.

Conclusion

Through linear regression techniques, we identified the feedbacks, dissociation of complexes, and negative regulators as the key components in apoptosis. The analysis and reduced models for our model formulation reveal that the chosen cell lines predominately exhibit strong extrinsic caspase, typical of type I cell, behavior. Furthermore, under the simplified model framework, the selected cells lines exhibit different modes by which caspase activation may occur. Finally the proposed modularized model of apoptosis may generalize behavior for additional cells and tissues, specifically identifying and predicting components responsible for the transition from type I to type II cell behavior.

The ubiquitin-proteasome and the mitochondria-associated apoptotic pathways are sequentially downregulated during recovery after immobilization-induced muscle atrophy

Immobilization produces morphological, physiological, and biochemical alterations in skeletal muscle leading to muscle atrophy and long periods of recovery. Muscle atrophy during disuse results from an imbalance between protein synthesis and proteolysis but also between apoptosis and regeneration processes. This work aimed to characterize the mechanisms underlying muscle atrophy and recovery following immobilization by studying the regulation of the mitochondria-associated apoptotic and the ubiquitin-proteasome-dependent proteolytic pathways. Animals were subjected to hindlimb immobilization for 4-8 days (I4 to I8) and allowed to recover after cast removal for 10-40 days (R10 to R40). Soleus and gastrocnemius muscles atrophied from I4 to I8 to a greater extent than extensor digitorum longus and tibialis anterior muscles. Gastrocnemius muscle atrophy was first stabilized at R10 before being progressively reduced until R40. Polyubiquitinated proteins accumulated from I4, whereas the increased ubiquitination rates and chymotrypsin-like activity of the proteasome were detectable from I6 to I8. Apoptosome and caspase-3 or -9 activities increased at I6 and I8, respectively. The ubiquitin-proteasome-dependent pathway was normalized early when muscle stops to atrophy (R10). By contrast, the mitochondria-associated apoptotic pathway was first downregulated below basal levels when muscle started to recover at R15 and completely normalized at R20. Myf 5 protein levels decreased from I4 to I8 and were normalized at R10. Altogether, our results suggest a two-stage process in which the ubiquitin-proteasome pathway is rapidly up- and downregulated when muscle atrophies and recovers, respectively, whereas apoptotic processes may be involved in the late stages of atrophy and recovery.

Mechanisms of N-acetyl cysteine-mediated protection from 2-hydroxyethyl methacrylate-induced apoptosis

Resin-based materials are now commonly used in dentistry in restorative materials as well as in endodontic sealers. These materials have been shown to be cytotoxic. The mechanisms by which resin-based materials mediate their adverse effects have not been completely elucidated. Here we show that 2-hydroxyethyl methacrylate (HEMA) induces apoptotic cell death in oral keratinocytes and immune cells through the intrinsic cell death pathway. Functional loss and cell death induced by HEMA was significantly inhibited in the presence of N-acetyl cysteine (NAC) treatment. In addition, HEMA induced a decrease in mitochondrial membrane potential, and an increase in cleaved caspases was potently inhibited in the presence of NAC treatment. Overall, the results reported in this article indicate that NAC is an effective chemoprotectant that can safely be used to protect the pulp and the surrounding tissues from adverse effects of dental restorative and endodontic materials.

Inhibition of apoptosome formation by suppression of Hsp90beta phosphorylation in tyrosine kinase-induced leukemias

Constitutively active tyrosine kinases promote leukemogenesis by increasing cell proliferation and inhibiting apoptosis. However, mechanisms underlying apoptotic inhibition have not been fully elucidated. In many settings, apoptosis occurs by mitochondrial cytochrome c release, which nucleates the Apaf-1/caspase-9 apoptosome. Here we report that the leukemogenic kinases, Bcr-Abl, FLT3/D835Y, and Tel-PDGFRbeta, all can inhibit apoptosome function. In cells expressing these kinases, the previously reported apoptosome inhibitor, Hsp90beta, bound strongly to Apaf-1, preventing cytochrome c-induced Apaf-1 oligomerization and caspase-9 recruitment. Hsp90beta interacted weakly with the apoptosome in untransformed cells. While Hsp90beta was phosphorylated at Ser 226/Ser 255 in untransformed cells, phosphorylation was absent in leukemic cells. Expression of mutant Hsp90beta (S226A/S255A), which mimics the hypophosphorylated form in leukemic cells, conferred resistance to cytochrome c-induced apoptosome activation in normal cells, reflecting enhanced binding of nonphosphorylatable Hsp90beta to Apaf-1. In Bcr-Abl-positive mouse bone marrow cells, nonphosphorylatable Hsp90beta expression conferred imatinib (Gleevec) resistance. These data provide an explanation for apoptosome inhibition by activated leukemogenic tyrosine kinases and suggest that alterations in Hsp90beta-apoptosome interactions may contribute to chemoresistance in leukemias.

Molecular cloning of novel Monad binding protein containing tetratricopeptide repeat domains

We have previously reported that Monad, a novel WD40 repeat protein, potentiates apoptosis induced by tumor necrosis factor-alpha(TNF-alpha) and cycloheximide (CHX). By affinity purification and mass spectrometry, we identified RNA polymerase II-associated protein 3 (RPAP3) as a binding protein of Monad. Overexpression of RPAP3 in HEK 293 potentiated caspase-3 activation and apoptosis induced by TNF-alpha and CHX. In addition, knockdown of RPAP3 by RNA interference resulted in a significant reduction of apoptosis induced by TNF-alpha and CHX in HEK293 and HeLa cells. These results raise the possibility that RPAP3, together with Monad, may function as a novel modulator of apoptosis pathway.

N-(4-Hydroxyphenyl)retinamide induced differentiation with repression of telomerase and cell cycle to increase interferon-gamma sensitivity for apoptosis in human glioblastoma cells

Glioblastoma is the most malignant and prevalent brain tumor in humans. It is composed of heterogenic abnormal astroglial cells that avoid differentiation, maintain proliferation, and hardly commit apoptosis. N-(4-Hydroxyphenyl)retinamide (4-HPR) induced astrocytic differentiation and increased sensitivity to interferon-gamma (IFN-gamma) for apoptosis in human glioblastoma A172, LN18, and SNB19 cells. Combination of 4-HPR and IFN-gamma significantly inhibited human telomerase reverse transcriptase (hTERT), cyclin dependent kinase 2 (CDK2), and survivin to up-regulate caspase-8, caspase-9, and caspase-3 for increasing apoptosis in all glioblastoma cell lines. Hence, combination of 4-HPR and IFN-gamma should be considered for controlling growth of different human glioblastoma cells.

Caspase activation cascades in apoptosis

Apoptosis, a highly controlled mode of cell death, is utilized to eliminate superfluous, aged, injured or infected cells from the body. Caspases, a family of aspartic acid-specific proteases, are the major effectors of apoptosis. To curtail their activity, caspases are normally synthesized as inactive precursors, but become activated at the onset of apoptosis by activation signals. Once active, caspases preside over the ordered dismantling of the cell through restricted proteolysis of hundreds of substrate proteins. Over the last 10 years, intense research has focused upon the pathways that control caspase activation. Although some, such as the apoptosome and death receptor-mediated pathways to caspase activation, are well established, others are less clearly defined. In this review, we discuss current perspectives concerning the diverse pathways to caspase activation.

Molecular mechanisms of apoptosis in cerebral ischemia: multiple neuroprotective opportunities

Cerebral ischemia/reperfusion (I/R) injury triggers multiple and distinct but overlapping cell signaling pathways, which may lead to cell survival or cell damage. There is overwhelming evidence to suggest that besides necrosis, apoptosis do contributes significantly to the cell death subsequent to I/R injury. Both extrinsic and intrinsic apoptotic pathways play a vital role, and upon initiation, these pathways recruit downstream apoptotic molecules to execute cell death. Caspases and Bcl-2 family members appear to be crucial in regulating multiple apoptotic cell death pathways initiated during I/R. Similarly, inhibitor of apoptosis family of proteins (IAPs), mitogen-activated protein kinases, and newly identified apoptogenic molecules, like second mitochondrial-activated factor/direct IAP-binding protein with low pI (Smac/Diablo), omi/high-temperature requirement serine protease A2 (Omi/HtrA2), X-linked mammalian inhibitor of apoptosis protein-associated factor 1, and apoptosis-inducing factor, have emerged as potent regulators of cellular apoptotic/antiapoptotic machinery. All instances of cell survival/death mechanisms triggered during I/R are multifaceted and interlinked, which ultimately decide the fate of brain cells. Moreover, apoptotic cross-talk between major subcellular organelles suggests that therapeutic strategies should be optimally directed at multiple targets/mechanisms for better therapeutic outcome. Based on the current knowledge, this review briefly focuses I/R injury-induced multiple mechanisms of apoptosis, involving key apoptotic regulators and their emerging roles in orchestrating cell death programme. In addition, we have also highlighted the role of autophagy in modulating cell survival/death during cerebral ischemia. Furthermore, an attempt has been made to provide an encouraging outlook on emerging therapeutic approaches for cerebral ischemia.

Apoptosis-inducing factor is a target for ubiquitination through interaction with XIAP

X-linked inhibitor of apoptosis (XIAP) is an inhibitor of apoptotic cell death that protects cells by caspase-dependent and independent mechanisms. In a screen for molecules that participate with XIAP in regulating cellular activities, we identified apoptosis-inducing factor (AIF) as an XIAP binding protein. Baculoviral IAP repeat 2 of XIAP is sufficient for the XIAP/AIF interaction, which is disrupted by Smac/DIABLO. In healthy cells, mature human AIF lacks only the first 54 amino acids, differing significantly from the apoptotic form, which lacks the first 102 amino-terminal residues. Fluorescence complementation and immunoprecipitation experiments revealed that XIAP interacts with both AIF forms. AIF was found to be a target of XIAP-mediated ubiquitination under both normal and apoptotic conditions, and an E3 ubiquitin ligase-deficient XIAP variant displayed a more robust interaction with AIF. Expression of either XIAP or AIF attenuated both basal and antimycin A-stimulated levels of reactive oxygen species (ROS), and when XIAP and AIF were expressed in combination, a cumulative decrease in ROS was observed. These results identify AIF as a new XIAP binding partner and indicate a role for XIAP in regulating cellular ROS.

TRAIL therapy in non-small cell lung cancer cells: sensitization to death receptor-mediated apoptosis by proteasome inhibitor bortezomib

Activation of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor pathway is a promising therapeutic strategy to selectively eradicate cancer cells, including non-small cell lung cancer (NSCLC) cells. Recombinant human (rh) TRAIL/Apo-2L, a TRAIL-encoding adenovirus, and monoclonal antibodies directed against TRAIL receptors R1 and R2 were used to study cytotoxicity of TRAIL therapy in NSCLC cells. NSCLC cells showed differential sensitivity to TRAIL therapy, regardless of the agent used. Combination treatment of bortezomib and rhTRAIL led to synergistic apoptosis induction in NSCLC cell lines. Enhancement of rhTRAIL-induced apoptosis by bortezomib was caspase dependent, implicating extrinsic as well as intrinsic apoptosis activation, as shown by increased processing of caspase-8 as well as caspase-9, and could be abrogated completely by overexpression of caspase-8 inhibitor cytokine response modifier A (CrmA), and partially by overexpression of Bcl-2. Enhanced surface expression of TRAIL-R2, but also TRAIL-R1, was associated with bortezomib treatment, which is likely to contribute to the increased processing of caspase-8 in the combination treatment. Furthermore, TRAIL-induced activation of prosurvival transcription factor nuclear factor-kappaB was prevented by cotreatment with bortezomib, which may contribute to the observed synergistic apoptosis induction. Our preclinical data indicate that combination therapy of TRAIL and bortezomib may be an effective strategy for NSCLC.

Procaspase-9 is attached to the mitochondrial outer membrane in the early stages of apoptosis

Procaspase-9 is the zymogen form of one of the apoptosis initiators, caspase-9. Its cellular location may differ depending on the cell type; it is found throughout the cytosol, although some of it may be associated with the mitochondria. Procaspase-9 relocates from the cytosol to the mitochondria shortly after the triggering of apoptosis in rat hepatocytes. We investigated whether the mitochondrial protein import machineries import procaspase-9. The combined results of protein import analyses, mitochondrial fractionation and protease treatments of intact and swollen mitochondria imply that procaspase-9 attaches to the outer surface of the mitochondrial outer membrane.

Nuclear Phospholipase C Gamma: Punctate Distribution and Association with the Promyelocytic Leukemia Protein

The marriage between transducers of cell stress stimuli and their nuclear targets is likely to be achieved in part by some spatial-temporal compartmentalization of the relevant effectors. A candidate compartment for these events is the promyelocytic leukemia nuclear domain (PML-ND), within which are found numerous effectors of damage recognition, repair, and cell death. We predicted that the identification of PML-ND cargo proteins would clarify those biochemical pathways that straddle the recognition of cellular damage and cell fate. We now use mass spectrometry of peptides eluted from PML coprecipitates to demonstrate that the gamma 1 (gamma1) isoform of PLC associates with nuclear PML. Though thought to act primarily in the cytoplasm, we use biochemical fractionation combined with immunocytochemistry to verify the nuclear expression of PLC-gamma1 and its interaction with PML. These are the first data to show an interaction between endogenous levels of a phosphoinositide metabolizing protein and the biophysically labile PML-ND by mass spectrometry and add weight to the view that PML-NDs may act as tumor suppressors by sequestering mitogenic effectors.

CB2 cannabinoid receptor agonist, JWH-015, triggers apoptosis in immune cells: potential role for CB2-selective ligands as immunosuppressive agents

Cannabinoids are known to interact with CB1 and CB2 receptors expressed in the nervous and immune system, respectively, and mediate a wide range of effects, including anti-inflammatory properties. However, cannabinoids that bind CB1 are also psychoactive thereby limiting their clinical use. In this study, we investigated the immunosuppressive properties of JWH-015, a synthetic CB2-selective agonist. We found that JWH-015 triggered apoptosis in thymocytes in vitro and inhibited the proliferative response of T and B cells to mitogens through induction of apoptosis. JWH-015 induced cross-talk between extrinsic and intrinsic pathways of apoptosis involving caspase-8, caspase-9, and caspase-3 as well as loss of mitochondrial membrane potential. Finally, administration of JWH-015 in vivo caused thymic atrophy, apoptosis, and decreased peripheral T cell response to mitogens. Together, this study suggests that CB2-selective agonists, devoid of psychotropic effect, may serve as novel anti-inflammatory/immunosuppressive agents.

Calcium blocks formation of apoptosome by preventing nucleotide exchange in Apaf-1

Apaf-1 plays an essential role in apoptosis. In the presence of cytochrome c and dATP, Apaf-1 assembles into an oligomeric apoptosome, which is responsible for the activation of procaspase-9 and the maintenance of the enzymatic activity of the processed caspase-9. Regulation of apoptosome assembly by other cellular factors is poorly understood. Here we report that physiological concentrations of calcium ion negatively affect the assembly of apoptosome by inhibiting nucleotide exchange in the monomeric, autoinhibited Apaf-1 protein. Consequently, calcium blocks the ability of Apaf-1 to activate caspase-9. These observations suggest an important role of calcium homeostasis on the Apaf-1-dependent apoptotic pathway.

Calcineurin potentiates the activation of procaspase-3 by accelerating its proteolytic maturation

We have previously shown that procaspase-3 exists in a high molecular weight complex in neonatal rat brain. Here, we purify and identify the protein that interacts with procaspase-3 from rat neonatal cortex. We searched binding proteins to procaspase-3 from a cytosolic extract of neonatal rat brain using chromatogram, two-dimensional gel electrophoresis, and far Western immunoblot. Analysis by tandem mass spectrometry identified the protein as a regulatory subunit of calcineurin (calcineurin B). Overexpression of calcineurin B in HEK293 cells potentiated processing of caspase-3 and apoptosis triggered by tumor necrosis factor-alpha and cycloheximide treatment. In a cell-free system, overexpression of calcineurin B in HEK293 cells markedly increased processing of caspase-3 by cytochrome c. Immunodepletion of calcineurin B from cytosolic extracts from Jurkat cells decreased processing of caspase-3 by cytochrome c. Knockdown of calcineurin B by RNA interference resulted in reduced apoptosis in HEK293 cells but not in caspase-3-deficient MCF-7 cells. These results suggest that calcineurin B potentiates the activation of procaspase-3 by accelerating its proteolytic maturation.

Effects of 4-hydroxy-2-nonenal on cultured human aortic endothelial cells and myocardial cell

To study the effects of 4-hydroxy-2-nonenal (HNE) on cultured human aortic endothelial cells and myocardial cells so as to explore the mechanism of the pathogenesis of atherosclerosis. In situ cell death technique, quantitative DNA damage detection and immunohistochemistry were used to identify the cell apoptosis and DNA damage in cultured human aortic endothelial cells and myocardial cells. Tail moment was 32.80+/-1.12, 44.30+/-0.99 and 74.6+/-0.97 when HAOEC were treated with 5 muM, 10muM and 15 muM of HNE for 10 hours, which were of statistical significance when compared with the normal group (6.0+/-0.67, P < 0.001 respectively), But when HAOEC was treated with 1 muM of HNE, the tail moment was 11.3+/-0.9, which was of no statistical difference compared with the untreated group(P>0.05). When human aortic endothelial cells (HAOEC) were treated with 5 muM, 10muM and 15 muM of HNE for 10 hours, the percent of nonviable cells were 5.70+/-0.55, 25.96+/-2.02 and 50.80+/-3.40 (P<0.001 respectively when compared with the normal group with the percent of 0.27+/-0.13). But when HAOEC was treated with 1 muM of HNE for 10 hours, the percent of nonviable cells was 2.5+/-0.22, and no difference was observed when compared with the untreated group (P>0.05). When cultured human myocardial cells were treated with 5 muM of HNE for 10 hours, TUNEL staining showed a greater number of apoptotic cells in HNE-treated human myocardial cells. No TUNEL-positive cells were observed in untreated group. When HAOEC was treated with 5 muM of HNE for 10 hours, immunocytochemical labeling with polyclonal antibody to HNE-modified proteins revealed specific cytoplasmic staining in cells incubated with HNE, whereas staining was absent in control cells incubated with vehicle. But 1 muM of HNE treatment didn't present positive stainings. Higher concentrations of HNE (10 muM and 15 muM) showed much stronger positive stainings. HNE induces DNA damage and cell apoptosis of cultured aortic endothelial cells and myocardial cells. The DNA damage and apoptosis levels are proportional to the HNE concentrations.

Role of loop bundle hydrogen bonds in the maturation and activity of (Pro)caspase-3

During maturation, procaspase-3 is cleaved at D175, which resides in a linker that connects the large and small subunits. The intersubunit linker also connects two active site loops that rearrange following cleavage and, in part, form the so-called loop bundle. As a result of chain cleavage, new hydrogen bonds and van der Waals contacts form among three active site loops. The new interactions are predicted to stabilize the active site. One unresolved issue is the extent to which the loop bundle residues also stabilize the procaspase active site. We examined the effects of replacing four loop bundle residues (E167, D169, E173, and Y203) on the biochemical and structural properties of the (pro)caspase. We show that replacing the residues affects the activity of the procaspase as well as the mature caspase, with D169A and E167A replacements having the largest effects. Replacement of D169 prevents caspase-3 autoactivation, and its cleavage at D175 no longer leads to an active enzyme. In addition, the E173A mutation, when coupled to a second mutation in the procaspase, D175A, may alter the substrate specificity of the procaspase. The mutations affected the active site environment as assessed by changes in fluorescence emission, accessibility to quencher, and cleavage by either trypsin or V8 proteases. High-resolution X-ray crystallographic structures of E167A, D173A, and Y203F caspases show that changes in the active site environment may be due to the increased flexibility of several residues in the N-terminus of the small subunit. Overall, the results show that these residues are important for stabilizing the procaspase active site as well as that of the mature caspase.

Engineered hybrid dimers: tracking the activation pathway of caspase-7

Caspase-7 is an obligate dimer of catalytic domains, with generation of activity requiring limited proteolysis within a region that separates the large and small chains of each domain. Using hybrid dimers we distinguish the relative contribution of each domain to catalysis by the whole molecule. We demonstrate that the zymogen arises from direct dimerization and not domain swapping. In contrast to previous conclusions, we show that only one of the catalytic domains must be proteolyzed to enable activation. The processed domain of this singly cleaved zymogen has the same catalytic activity as a domain of fully active caspase-7. A transient intermediate of singly cleaved dimeric caspase-7 can be found in a cell-free model of apoptosis induction. However, we see no evidence for an analogous intermediate of the related executioner caspase-3. Our study demonstrates the efficiency by which the executioner caspases are activated in vivo.

Apoptosome: a platform for the activation of initiator caspases

Apoptosome refers to the adaptor protein complex that mediates the activation of an initiator caspase at the onset of apoptosis. In mammalian cells, caspase-9, caspase-8, and caspase-2 rely on the apoptotic protease-activating factor 1 (Apaf-1)-apoptosome, death-inducing signaling complex (DISC), and PIDDosome, respectively, for activation. In Drosophila, activation of the caspase-9 homolog Dronc requires assembly of an apoptosome comprised of Dark/Hac-1/Dapaf-1. In Caenorhabditis elegans, activation of the caspase CED-3 is facilitated by the CED-4-apoptosome. Recent biochemical and structural investigation revealed significant insights into the assembly and function of the various apoptosomes. Nonetheless, conclusive mechanisms by which the initiator caspases are activated by the apoptosomes remain elusive. Several models have been proposed to explain the activation process. The induced proximity model summarizes the general process of initiator caspase activation. The proximity-driven dimerization model describes how initiator caspases respond to induced proximity and offers an explanation for their activation. Regardless of how initiator caspases are activated, enhanced activity must be correlated with altered active site conformation. The induced conformation model posits that the activated conformation for the active site of a given initiator caspase is attained through direct interaction with the apoptosome or through homo-oligomerization facilitated by the apoptosome.

Dynamic changes of apoptosis and expression of Bcl-2 family members in the posthatch hippocampus of Bengalese finches

The hippocampus of songbirds plays an important role in spatial memory, and probably in song learning. Although prolonged neuronal generation and apoptosis are thought to be closely correlated with memory function, natural changes of the number of neurons and in apoptosis in the hippocampus of songbirds have not been fully investigated during development and in the adult. In the current study, we examined developmental changes in the volume and the number of neurons and apoptotic cells in the hippocampus of songbirds (Lonchura striata) from posthatch day (P5) to adulthood. Apoptotic cells were determined by Nissl staining and immunohistochemistry for cleaved caspase-3, a key apoptotic caspase executioner. The expression levels of Bcl-2 family member mRNA and protein, including Bcl-2, Bcl-xL and Bax, were also investigated. Our results indicated that: (1) the hippocampus volume significantly increased from P5 to P60, although the number of neurons remained stable in all studied stages; (2) the number of apoptotic cells was highest at P45, based either on the Nissl staining or on the immunohistochemistry for caspase-3; (3) Bcl-2 mRNA expression was high from P5 to adulthood, while Bax mRNA declined abruptly from P5 to adulthood, and Bcl-x mRNA was high after P45. Bcl-2 protein was only detected at P5 and P15, while detection of Bcl-xL and Bax proteins paralleled levels of mRNA expression. Our study provides detailed changes of apoptosis in the posthatch songbird hippocampus, suggesting an important role for caspase-3 and Bcl-2 family members in hippocampus apoptosis.

Activation of Caspases in Human Spermatozoa during Cryopreservation – An Immunoblot Study

Cellular stress to ejaculated spermatozoa such as cryopreservation is known to induce caspase-derived, apoptotic signaling. Therefore, the proenzymes and active forms of caspases 1, 3, 8 and 9 were examined by western blot technique in unfrozen and frozen human spermatozoa of infertility patients and of healthy donors. Twenty-two semen samples derived from healthy donors and 26 semen samples of unselected infertility patients were divided into 3 parts, two of them were cryostored at -196 degrees C with 7% or 14% (v/v, final concentration) of glycerol. The caspases were detected by immunoblots with polyclonal rabbit-anti-caspases-antibodies after 15% sodium dodecyl sulfate-polyacrylgel electrophoresis (SDS-PAGE) under reducing conditions. For evaluation of the differences between amounts of caspase protein the luminol/H(2)O(2) method was applied. A significant increase of activated caspase-1 in donors, of caspase-8 in patients and caspase-9 in patients and donors after cryopreservation were found, whereas, the application of 14% glycerol resulted in higher amounts of activated caspase than did 7% glycerol. Possibly, glycerol may also contribute to activation of caspases via direct toxic effects to mitochondria during cryopreservation of spermatozoa. This finding strongly supports an hypothesis of a higher mitochondria-derived apoptosis-sensitivity of spermatozoa in patients than in healthy donors during cryopreservation. Inactive caspase-3 was reduced subsequent to cryopreservation in patients (p<0.05) and non-significant in donors (p<0.05). Active caspase-3 was detectable in all samples but without significant differences between the three assays. It is concluded that mechanisms associated with apoptotic processes deserve attention in cryopreservation of spermatozoa in order to conserve vital sperm functions after thawing.

Programmed cell death mechanisms of identifiable peptidergic neurons in Drosophila melanogaster

The molecular basis of programmed cell death (PCD) of neurons during early metamorphic development of the central nervous system (CNS) in Drosophila melanogaster are largely unknown, in part owing to the lack of appropriate model systems. Here, we provide evidence showing that a group of neurons (vCrz) that express neuropeptide Corazonin (Crz) gene in the ventral nerve cord of the larval CNS undergo programmed death within 6 hours of the onset of metamorphosis. The death was prevented by targeted expression of caspase inhibitor p35, suggesting that these larval neurons are eliminated via a caspase-dependent pathway. Genetic and transgenic disruptions of ecdysone signal transduction involving ecdysone receptor-B (EcR-B) isoforms suppressed vCrz death, whereas transgenic re-introduction of either EcR-B1 or EcR-B2 isoform into the EcR-B-null mutant resumed normal death. Expression of reaper in vCrz neurons and suppression of vCrz-cell death in a reaper-null mutant suggest that reaper functions are required for the death, while no apparent role was found for hid or grim as a death promoter. Our data further suggest that diap1 does not play a role as a central regulator of the PCD of vCrz neurons. Significant delay of vCrz-cell death was observed in mutants that lack dronc or dark functions, indicating that formation of an apoptosome is necessary, but not sufficient, for timely execution of the death. These results suggest that activated ecdysone signaling determines precise developmental timing of the neuronal degeneration during early metamorphosis, and that subsequent reaper-mediated caspase activation occurs through a novel DIAP1-independent pathway.

A mathematical model for apoptosome assembly: the optimal cytochrome c/Apaf-1 ratio

Apoptosis, a highly conserved form of cell suicide, is regulated by apoptotic signals and their transduction with caspases, a family of cystein proteases. Caspases are constantly expressed in the normal cells as inactive pro-enzymes. The activity of caspase is regulated by the proteolysis. Sequential proteolytic reactions of caspases are needed to execute apoptosis. Mitochondrial pathway is one of these apoptotic signal pathways, in which caspases are oligomerized into characteristic heptamer structure, called apoptosome, with caspase-9 that activate the effector caspases for apoptosis. To investigate the dynamics of signal transduction pathway regulated by oligomerization, we construct a mathematical model for Apaf-1 heptamer assembly process. The model first reveals that intermediate products can remain unconverted even after all assemble reactions are completed. The second result of the model is that the conversion efficiency of Apaf-1 heptamer assembly is maximized when the initial concentration of cytochrome c is equal to that of Apaf-1. When the concentration of cytochrome c is sufficiently larger or smaller than that of Apaf-1, the final Apaf-1 heptamer production is decreased, because intermediate Apaf-1 oligomers (tetramers and bigger oligomers), which themselves are unable to form active heptamer, accumulate too fast in the cells, choking a smooth production of Apaf-1 heptamer. Slow activation of Apaf-1 monomers and small oligomers increase the conversion efficiency. We also study the optimal number of subunits comprising an active oligomer that maximize the conversion efficiency in assembly process, and found that the tetramer is the optimum.

Monad, a WD40 repeat protein, promotes apoptosis induced by TNF-α

WD40 repeat proteins have a wide range of diverse biological functions including signal transduction, cell cycle regulation, RNA splicing, and transcription. Here we report the identification and characterization of a novel human WD40 repeat protein, Monad. Monad is unique, since it contains only two WD40 repeats. Monad is widely expressed in human tissues with the highest expression in testis. Overexpression of Monad in HEK293 cells potentiated apoptosis and caspase-3 activation induced by tumor necrosis factor-alpha and cycloheximide. These results raise the possibility that Monad may function as a novel modulator of apoptosis pathway.

An efficient method to express and refold a truncated human procaspase-9: A caspase with activity toward Glu-X bonds

A truncated form of human procaspase-9 missing the first 111 amino acids, and a variety of mutants derived therefrom, have been expressed in Escherichia coli inclusion bodies. Upon refolding to active enzymes, Delta(1-111) procaspase-9 and mutants were recovered at purity greater than 95% and with a final yield of 20-35 mg/L cell culture. Our active procaspase-9 retains its pro-segment, while undergoing major auto processing at Asp315 and a minor (20%) cleavage at Glu306. This unusual cleavage at a Glu-X bond also took place in the D315E mutant, and we describe herein the inhibitor Z-VAE-fmk that shows enhanced inactivation of procaspase-9 over caspases-3. The bond at Asp330, not processed by procaspase-9, is cleaved by caspase-3 and the resulting procaspase-9 variant, missing the 316-330 bridge, is six times as active as the non-mutated Delta(1-111) proenzyme. A deletion mutant lacking residues 316-330 underwent auto activation by cleavage at Asp315-Ala331 bond. Moreover, substitution of Glu306 by an Asp residue in this mutant led to rapid removal of the peptide spanning Ser307 to Asp330, and resulted in an enzyme that was 7.6 times as active as the non-mutated Delta(1-111) procaspase-9. Finally, replacing both Asp315 and Glu306 with Ala generated a procaspase-9 mutant incapable of auto processing. This single chain procaspase-9 was fully as active as the non-mutated Delta(1-111) enzyme processed at Asp315 or Glu306. Our demonstration that unprocessed procaspase-9 mutants are active as proteases with caspase-type specificity suggests that the role of procaspase-9 in cascade activation of executioner caspases might, in some circumstances, be carried out alone and without association of the apoptosome.

The role of cellular flice inhibitory protein (c-FLIP) in the pathogenesis and treatment of cancer

Protection from death receptor (DR)-mediated apoptosis has been proposed as an important step in the development of malignancy, enabling tumour cells not only to survive and escape antitumour immune responses, but also to develop resistance to chemotherapy or other cancer treatments. An important regulator of DR-induced death is the cellular FADD-like IL-1beta-converting enzyme inhibitory protein (c-FLIP) which, when overexpressed, can protect tumour cells from apoptosis. This review focuses on the role of c-FLIP as a tumour progression factor, with particular emphasis on recent work from the authors' laboratory concerning the contribution of c-FLIP to the pathogenesis of Hodgkin's lymphoma. The possibility of targeting c-FLIP as an approach to the treatment of cancer and, in particular, Hodgkin's lymphoma is discussed.

2-(4-methylphenyl)-1,3-selenazol-4-one induces apoptosis by different mechanisms in SKOV3 and HL 60 cells

We examined the ability of the synthetic selenium compound, 2-(4-methylphenyl)-1,3-selenazol-4-one (hereafter designated 3a), to induce apoptosis in a human ovarian cancer cell line (SKOV3) and a human leukemia cell line (HL-60). Flow cytometry showed that 3a treatment induced apoptosis in both cell lines to degrees comparable to that of the positive control, paclitaxel. Apoptosis was measured by PS externalization, DNA fragmentation and decreased mitochondrial membrane potential (MMP). However, analysis of the mechanism of action revealed differences between the responses of the two cell lines. Treatment with 3a arrested the cell cycle and induced caspase-3 activation in HL-60 cells, but not in SKOV3 cells. In contrast, 3a treatment induced apoptosis through translocation of AIF, a novel pro-apoptotic protein, in SKOV3 cells, but not in HL-60 cells. Collectively, our data demonstrated that 3a induced apoptosis in both cell lines, but via different action mechanisms.