Apoptosis-independent functions of killer caspases

Balancing between apoptosis and survival biomarkers in the patients with tuberculous meningitis

BACKGROUND

The balancing factor of apoptosis, survival, inflammatory and oxidative stress biomarkers may determine the clinico-radiological severity and death in the patients with tuberculous meningitis (TBM).

AIM

We report the relationship of death [caspase-3, malondialdehyde (MDA), tumor necrosis factor-α (TNFα), interleukin 6 (IL6)] and survival biomarkers [X-linked inhibitory apoptotic protein (XIAP), IL10, glutathione (GSH) and catalase] in TBM, and its role in determining disease severity and death.

METHODS

The diagnosis of TBM was based on clinical, MRI and cerebrospinal fluid (CSF) findings. Their clinical and MRI findings were noted. The severity of TBM was categorized as stages I to III. Serum and CSF caspase-3 and XIAP were measured by ELISA, and TNFα, IL6 and IL10 gene expression in peripheral blood mononuclear cells using RT-PCR (reverse-transcriptase polymerase chain reaction). Plasma MDA, GSH and catalase were measured by spectrophotometer.

RESULTS

There were 40 patients with TBM whose mean age was 31.6 years and 50% were females. TBM patients had higher expression of death (caspase-3, TNFα, IL6, and MDA) and suppression of survival biomarkers (XIAP, catalase and GSH) compared to the healthy controls. Caspase-3 positively correlated with TNFα, IL6 and MDA, and negatively with XIAP, GSH and catalase. Patients with longer duration of illness and definite TBM had higher expression of caspase-3. Patients who died has higher expression of caspase-3 and suppression of XIAP compared to those who survived.

CONCLUSION

It can be concluded from this study that there is up-regulation of death signals and suppression of survival signals in TBM.

Ars moriendi: Proteases as sculptors of cellular suicide

The Ars moriendi, which translates to "The Art of Dying," encompasses two Latin texts that gave advice on how to die well and without fear according to the Christian precepts of the late Middle Ages. Given that ten to hundred billion cells die in our bodies every day, it is obvious that the concept of a well and orderly ("regulated") death is also paramount at the cellular level. In apoptosis, as the most well-studied form of regulated cell death, proteases of the caspase family are the central mediators. However, caspases are not the only proteases that act as sculptors of cellular suicide, and therefore, we here provide an overview of the impact of proteases in apoptosis and other forms of regulated cell death.

Dynamics of cell death across growth stages and the diel cycle in the dinoflagellate Karenia brevis

Recent evidence suggests that programmed cell death (PCD) can play a role in stress-induced decline and termination of harmful algal blooms. However, components of the PCD cascade, i.e. reactive oxygen species (ROS) and caspase-like activity, have also been observed in the absence of exogenous stress, where their activities and functions remain unclear. Here, we characterized the variability of prevalence of cell death, ROS, and caspase-like activity at different growth phases and diel cycles in cultures of dinoflagellate Karenia brevis. Results show that ROS percentages increased with culture age and fluctuated in a phasing diel pattern, while caspase-like activity was observed throughout growth. In actively growing K. brevis cells, PCD components may be involved in key metabolic processes, while in stationary phase they may relate to stress acclimation. The circadian diel pattern of ROS may be explained by the balance between the metabolic generation of ROS and circadian rhythmicity of antioxidant enzymes. Overall, this work highlights not only the involvement of PCD components in the growth of marine phytoplankton, but the importance of understanding mechanisms controlling their accumulation, which would help to better interpret their presence in the field.

Anastasis: Return Journey from Cell Death

For over 20 years, it has been a dogma that once the integrity of mitochondria is disrupted and proapoptotic proteins that are normally located in the intermembrane space of mitochondria appeared in the cytoplasm, the process of cell death becomes inevitable. However, it has been recently shown that upon removal of the death signal, even at the stage of disturbance in the mitochondria, cells can recover and continue to grow. This phenomenon was named anastasis. Here, we will critically discuss the present knowledge concerning the mechanisms of cell death reversal, or development of anastasis, methods for its detection, and what role signaling from different intracellular compartments plays in anastasis stimulation.

The metabolite 5-methyl-1,3-benzenediol and its derivative methyl-2,4-dihydroxy-6-methylbenzoate from the lichen Parmotrema tinctorum with potent apoptotic and anti-angiogenesis effects

Nature has been a rich resource of novel anticancer agents, one such source being lichens, which represent the symbiosis between algae and fungi with diverse range of secondary metabolites having therapeutic significance. With respect to this, the present study evaluates the in vitro apoptogenic profile of secondary metabolites from the lichen Parmotrema tinctorum towards cancer cell lines. Treatment with TLC-purified fraction 1 from P. tinctorum resulted in significant reduction in the cell viabilities of cancer cells with IC50 values ranging between 1.2 and 12.8 μg/ml. The potential anticancer effect of the bioactive fraction was further supported by Trypan blue cell viability, LDH and DNA fragmentation assays. At the cellular level, induction of apoptosis was confirmed through the activation of the caspase cascade and apoptotic cells accumulating in the Sub-G1 phase of cell cycle. Angiogenesis being one of the major characteristics needed for cancer growth, the ability of the lichen fraction to inhibit angiogenesis was checked through in ovo Yolk Sac Membrane (YSM) assay and was found to be significant. The study also verified the non-toxic nature of the bioactive fraction towards normal human peripheral lymphocytes. HPLC analysis and GC-MS characterisation of the bioactive fraction indicated the presence of 5-methyl-1,3-benzenediol and its derivative methyl-2,4-dihydroxy-6-methylbenzoate.

Intertwined Functions of Separase and Caspase in Cell Division and Programmed Cell Death

Timely sister chromatid separation, promoted by separase, is essential for faithful chromosome segregation. Separase is a member of the CD clan of cysteine proteases, which also includes the pro-apoptotic enzymes known as caspases. We report a role for the C. elegans separase SEP-1, primarily known for its essential activity in cell division and cortical granule exocytosis, in developmentally programmed cell death when the predominant pro-apoptotic caspase CED-3 is compromised. Loss of SEP-1 results in extra surviving cells in a weak ced-3(-) mutant, and suppresses the embryonic lethality of a mutant defective for the apoptotic suppressor ced-9/Bcl-2 implicating SEP-1 in execution of apoptosis. We also report apparent non-apoptotic roles for CED-3 in promoting germ cell proliferation, meiotic chromosome disjunction, egg shell formation, and the normal rate of embryonic development. Moreover, loss of the soma-specific (CSP-3) and germline-specific (CSP-2) caspase inhibitors result in CED-3-dependent suppression of embryonic lethality and meiotic chromosome non-disjunction respectively, when separase function is compromised. Thus, while caspases and separases have evolved different substrate specificities associated with their specialized functions in apoptosis and cell division respectively, they appear to have retained the residual ability to participate in both processes, supporting the view that co-option of components in cell division may have led to the innovation of programmed cell suicide early in metazoan evolution.

Shikonin sensitizes A549 cells to TRAIL-induced apoptosis through the JNK, STAT3 and AKT pathways

BACKGROUND

TRAIL, tumor necrosis factor-related apoptosis-inducing ligand, can selectively kill cancer cells with little or no cytotoxicity toward normal human cells and is regarded as a potential relatively safe antitumor drug. However, some cancer cells are resistant to TRAIL-induced apoptosis. Thus, reagents that potentiate TRAIL-induced cytotoxicity are needed. Herein, we investigated whether shikonin, a natural compound from the root of Lithospermum erythrorhizon, can sensitize TRAIL-resistant cells to TRAIL-induced cytotoxicity.

RESULTS

The viability of A549 cells, which were resistant to TRAIL, was significantly decreased after treatment with TRAIL followed by shikonin. The underlying mechanisms by which shikonin sensitizes cells to TRAIL-induced cytotoxicity were also examined. Combined treatment with shikonin and TRAIL activated the caspase and JNK pathways, inhibited the STAT3 and AKT pathways, downregulated the expression of Mcl-1, Bcl-2, Bcl-xL, c-FLIP and XIAP and upregulated the expression of Bid.

CONCLUSIONS

In conclusion, the results indicated that shikonin sensitized resistant cancer cells to TRAIL-induced cytotoxicity via the modulation of the JNK, STAT3 and AKT pathways, the downregulation of antiapoptotic proteins and the upregulation of proapoptotic proteins.

High Frequencies of Caspase-3 Expressing Mycobacterium tuberculosis-Specific CD4+ T Cells Are Associated With Active Tuberculosis

Antigen-specific CD4⁺ T cell responses to Mycobacterium tuberculosis (Mtb) infection are important for host defense against tuberculosis (TB). However, Mtb-specific IFN-γ-producing T cells do not distinguish active tuberculosis (ATB) patients from individuals with asymptomatic latent Mtb infection (LTBI). We reasoned that the immune phenotype of Mtb-specific IFN-γ⁺CD4⁺ T cells could provide an indirect gauge of Mtb antigen load within individuals. We sought to identify immune markers in Mtb-specific IFN-γ⁺CD4⁺ T cells and hypothesized that expression of caspase-3 Mtb-specific CD4⁺ T cells would be associated with ATB. Using polychromatic flow cytometry, we evaluated the expression of caspase-3 in Mtb-specific CD4⁺ T cells from LTBI and ATB as well as from ATB patients undergoing anti-TB treatment. We found significantly higher frequencies of Mtb-specific caspase-3⁺IFN-γ⁺CD4⁺ T cells in ATB compared to LTBI. Caspase-3⁺IFN-γ⁺CD4⁺ T cells were also more activated compared to their caspase-3-negative counterparts. Furthermore, the frequencies of caspase-3⁺IFN-γ⁺CD4⁺ T cells decreased in response to anti-TB treatment. Our studies suggest that the frequencies of caspase-3-expressing antigen-specific CD4⁺ T cells may reflect mycobacterial burden in vivo and may be useful for distinguishing Mtb infection status along with other host biomarkers.

Inhibitory effect of oxymatrine on hepatocyte apoptosis via TLR4/PI3K/Akt/GSK-3β signaling pathway

AIM

To evaluate the effect of oxymatrine (OMT) on hepatocyte apoptosis in rats with lipopolysaccharide (LPS)/D-galactosamine (D-GalN)-induced acute liver failure (ALF).

METHODS

LPS/D-GalN was used to establish a model of ALF in rats. To evaluate the effect of OMT, we assessed apoptosis by transmission electron microscopy, and the pathological changes in the liver by light microscopy with hematoxylin and eosin staining. An automated biochemical analyzer was used to measure serum alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Enzyme-linked immunosorbent assay was used to determine the levels of tumor necrosis factor (TNF)-α and interleukin (IL)-1β. Western blotting was used to detect protein levels in liver tissues. Streptavidin peroxidase immunohistochemistry was used to observe expression of Toll-like receptor (TLR)4, active caspase-3, Bax and Bcl-2.

RESULTS

All rats in the normal control and OMT-pretreated groups survived. The mortality rate in the model group was 30%. OMT preconditioning down-regulated apoptosis of hepatocytes and ameliorated pathological changes in liver tissue. The levels of AST, ALT, TNF-α and IL-1β in the model group increased significantly, and were significantly reduced by OMT pretreatment. OMT pretreatment down-regulated expression of TLR4 and active caspase-3 and the Bax/Bcl-2 ratio, and up-regulated expression of P-Akt^Ser473 (Akt phosphorylated at serine 473) and P-GSK3β^Ser9 (glycogen synthase kinase 3β phosphorylated at serine 9) induced by LPS/D-GalN.

CONCLUSION

OMT inhibits hepatocyte apoptosis by suppressing the TLR4/PI3K/Akt/GSK-3β signaling pathway, which suggests that OMT is an effective candidate for ameliorating acute liver failure.

Mitochondria-Targeted Antioxidant SkQR1 Reduces TNF-Induced Endothelial Permeability in vitro

Prolonged or excessive increase in the circulatory level of proinflammatory tumor necrosis factor (TNF) leads to abnormal activation and subsequent damage to endothelium. TNF at high concentrations causes apoptosis of endothelial cells. Previously, using mitochondria-targeted antioxidants of SkQ family, we have shown that apoptosis of endothelial cells is dependent on the production of reactive oxygen species (ROS) in mitochondria (mito-ROS). Now we have found that TNF at low concentrations does not cause cell death but activates caspase-3 and caspase-dependent increase in endothelial permeability in vitro. This effect is probably due to the cleavage of β-catenin - an adherent junction protein localized in the cytoplasm. We have also shown that extracellular matrix metalloprotease 9 (MMP9) VE-cadherin shedding plays a major role in the TNF-induced endothelial permeability. The mechanisms of the caspase-3 and MMP9 activation are probably not related to each other since caspase inhibition did not affect VE-cadherin cleavage and MMP9 inhibition had no effect on the caspase-3 activation. Mitochondria-targeted antioxidant SkQR1 inhibited TNF-induced increase in endothelial permeability. SkQR1 also inhibited caspase-3 activation, β-catenin cleavage, and MMP9-dependent VE-cadherin shedding. The data suggest that mito-ROS are involved in the increase in endothelial permeability due to the activation of both caspase-dependent cleavage of intracellular proteins and of MMP9-dependent cleavage of the transmembrane cell-to-cell contact proteins.

Extracellular 2'5'-oligoadenylate synthetase 2 mediates T-cell receptor CD3-ζ chain down-regulation via caspase-3 activation in oral cancer

Decreased expression of CD3-ζ chain, an adaptor protein associated with T-cell signalling, is well documented in patients with oral cancer, but the mechanistic justifications are fragmentary. Previous studies in patients with oral cancer have shown that decreased expression of CD3-ζ chain was associated with decreased responsiveness of T cells. Tumours are known to induce localized as well as systemic immune suppression. This study provides evidence that oral tumour-derived factors promote immune suppression by down-regulating CD3-ζ chain expression. 2'5'-Oligoadenylate synthetase 2 (OAS2) was identified by the proteomic approach and our results established a causative link between CD3-ζ chain down-regulation and OAS2 stimulation. The surrogate situation was established by over-expressing OAS2 in a HEK293 cell line and cell-free supernatant was collected. These supernatants when incubated with T cells resulted in down-regulation of CD3-ζ chain, which shows that the secreted OAS2 is capable of regulating CD3-ζ chain expression. Incubation of T cells with cell-free supernatants of oral tumours or recombinant human OAS2 (rh-OAS2) induced caspase-3 activation, which resulted in CD3-ζ chain down-regulation. Caspase-3 inhibition/down-regulation using pharmacological inhibitor or small interfering RNA restored down-regulated CD3-ζ chain expression in T cells induced by cell-free tumour supernatant or rh-OAS2. Collectively these results show that OAS2 leads to impairment in CD3-ζ chain expression, so offering an explanation that might be applicable to the CD3-ζ chain deficiency observed in cancer and diverse disease conditions.

Role of TLR4-Mediated PI3K/AKT/GSK-3β Signaling Pathway in Apoptosis of Rat Hepatocytes

We investigated the mechanism of the Toll-like receptor 4- (TLR4-) mediated PI3K/AKT/GSK-3β signaling pathway in rat hepatocytes apoptosis induced by LPS. The cultured rat hepatocytes were treated with LPS alone or first pretreated with TLR4 inhibitor, AKT inhibitor, and GSK-3β inhibitor, respectively, and then stimulated with the same dose of LPS. Cell viability, cell apoptotic rate, and apoptosis morphology were assessed; the level of P-AKT^Ser473, P-GSK-3β^Ser9, and active Caspase-3 and the ratio of Bax/Bcl-2 were evaluated. The results indicated that cell viability decreased, while cell apoptotic rate increased with time after LPS stimulation. The expression of P-AKT^Ser473 and P-GSK-3β^Ser9 in the LPS group decreased compared with the control, while the level of active Caspase-3 and the ratio of Bax/Bcl-2 were significantly increased. These effects were attenuated by pretreatment with CLI-095. In addition, the apoptotic ratio decreased after pretreatment with LiCl but increased following pretreatment with LY294002. The expression of P-AKT^Ser473 further decreased following pretreatment with LY294002 and the expression of P-GSK-3β^Ser9 increased following pretreatment with LiCl. Moreover, pretreatment with CLI-095 weakened LPS-induced nuclear translocation of GSK-3β. Our findings suggest that the TLR4-mediated PI3K/AKT/GSK-3β signaling pathway is present in rat hepatocytes and participates in apoptosis of BRL-3A cells.

Mice Lacking Functional Fas Death Receptors Are Protected from Kainic Acid-Induced Apoptosis in the Hippocampus

The Fas receptor (FasR)/Fas ligand (FasL) system plays a significant role in the process of neuronal loss in neurological disorders. Thus, in the present study, we used a real-time PCR array focused apoptosis (Mouse Apoptosis RT(2) PCR Array) to study the role of the Fas pathway in the apoptotic process that occurs in a kainic acid (KA) mice experimental model. In fact, significant changes in the transcriptional activity of a total of 23 genes were found in the hippocampus of wild-type C57BL/6 mice after 12 h of KA treatment compared to untreated mice. Among the up-regulated genes, we found key factors involved in the extrinsic apoptotic pathway, such as tnf, fas and fasL, and also in caspase genes (caspase -4, caspase-8 and caspase-3). To discern the importance of the FasR/FasL pathway, mice lacking the functional Fas death receptor (lpr) were also treated with KA. After 24 h of neurotoxin treatment, lpr mice exhibited a reduced number of apoptotic positive cells, determined by the terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) method in different regions of the hippocampus, when compared to wild-type mice. In addition, treatment of lpr mice with KA did not produce significant changes in the transcriptional activity of genes related to apoptosis in the hippocampus, either in the fas and fas ligand genes or in caspase-4 and caspase-8 and the executioner caspase-3 genes, as occurred in wild-type C57BL/6 mice. Thus, these data provide direct evidence that Fas signalling plays a key role in the induction of apoptosis in the hippocampus following KA treatment, making the inhibition of the death receptor pathway a potentially suitable target for excitotoxicity neuroprotection in neurological conditions such as epilepsy.

Identification of a secondary promoter of CASP8 and its related transcription factor PURα

Caspase-8 (CASP8) is an essential initiator of apoptosis and is associated with many diseases in humans including esophageal squamous cell carcinoma. CASP8 produces a variety of transcripts, which might perform distinct functions. However, the cis and trans transcriptional determinants that control CASP8 expression remain poorly defined. Using a series of luciferase reporter assays, we identified a novel secondary promoter of CASP8 within chr2: 202,122,236 to 202,123,227 and 25 kb downstream of the previously described CASP8 promoter. ENCODE ChIP-seq data for this novel promoter region revealed several epigenetic features, including high levels of histone H3 lysine 27 acetylation and lysine 4 methylation, as well as low levels of CpG island methylation. We developed a mass spectrometry based strategy to identify transcription factors that contribute to the function of the secondary promoter. We found that the transcription activator protein PURα is specifically involved in the transcriptional activation of the secondary promoter and may exert its function by forming a complex with E2F-1 and RNA polymerase II. PURα can bind to both DNA and RNA, and functions in the initiation of DNA replication, regulation of transcription. We observed that knockdown of PURα expression decreased the transcriptional activity of the secondary promoter and mRNA expression of CASP8 isoform G. Although the physiologic roles of this secondary promoter remain unclear, our data may help explain the complexity of CASP8 transcription and suggest that the various caspase 8 isoforms may have distinct regulations and functions.

Understanding the conservation patterns and molecular phylogenetics of human death receptors family through computational biology

Human death receptors (TNFR1, FAS, DR3, DR4, DR5, DR6 and TNFBR), primarily from tumor necrosis receptor super family, play an essential role in the process of the extrinsic pathway of apoptosis. We performed conserved domain, amino acid residues analysis in which cysteine residues were found to be highly conserved for all the family members. Sixteen (16) highly conserved residues were observed in TNFR1, DR3 and TNFBR; and in case of Fas, only seven (7) residues are highly conserved. From molecular phylogenetics, we found that DR5 and DR4, TNFR1 and DR3 and TNFR1 and DR3 had the same point of origin. Alternatively, Fas was found to be distant from the rest of the death receptors. A network map was developed to explain these proteins are not only interlinked among themselves, but also interlinked with several other proteins. We have also observed from this system that scores of all the nodes ranges from 0.996 to 0.999.

The Spodoptera frugiperda effector caspase Sf-caspase-1 becomes unstable following its activation

Sf-caspase-1 is the principal effector caspase in Spodoptera frugiperda cells. Like the caspases in other organisms, Sf-caspase-1 is processed by upstream caspases to form an active heterotetramer composed of the p19 and p12 subunits. The regulation of active caspases is crucial for cellular viability. In mammal cells, the subunits and the active form of caspase-3 were rapidly degraded relative to its proenzyme form. In the present study, the S. frugiperda Sf9 cells were transiently transfected with plasmids encoding different fragments of Sf-caspase-1: the pro-Sf-caspase-1 (p37), a prodomain deleted fragment (p31), a fragment containing the large subunit and the prodomain (p25), the large subunit (p19), and the small subunit (p12). Flow cytometry and Western blot analysis revealed that p12, p19, and p25 were unstable in the transfected cells, in contrast to p37 and p31. Lactacystin, a proteasome inhibitor, increased the accumulation of the p19 and p12 subunits, suggesting that the degradation is performed by the ubiquitin-proteasome system. During the activation, the Sf-caspase-1 produces an intermediate form and then undergoes proteolytic processing to form active Sf-caspase-1. We found that both the active and the intermediate form were unstable, indicating that once activated or during its activation, the Sf-caspase-1 was unstable.

Stress-related responses in Alexandrium tamarense cells exposed to environmental changes

Organisms tend to be sensitive to drastic changes in environmental conditions. For unicellular microorganisms, variations in physico-chemical conditions are particularly challenging and may result in acclimation, entrance into quiescence, or death through necrotic or autocatalytic pathways. This study focuses on the thecate dinoflagellate Alexandrium tamarense. Cellular responses to oxidative, thermal, and nutrient stress were characterized using stress indicators, such as pigment content, efficiency of photosystem II or production of reactive oxygen species (ROS), as well as hallmarks of apoptosis including activity of caspase-like enzymes and expression of a metacaspase gene homolog. The formation of temporary cysts, a survival strategy of short-term quiescence, was also monitored. Cellular responses appeared to depend on multifactorial influences where type and intensity of stimulus as well as position in cell cycle may act in combination. Sequences of events observed implicate ROS production as a key determinant of stress-related pathways, playing potential roles in intracellular signaling, formation of temporary cysts, or cellular damage. Variations observed in caspase-like activities and metacaspase gene expression did not appear to be associated with programmed cell death pathways; our results suggest a wider range of functions for these proteases in phytoplankton cells, including roles in survival pathways and cell cycle progression.

Mechanical forces stimulate endothelial microparticle generation via caspase-dependent apoptosis-independent mechanism

Microparticle release by vascular endothelium has been implicated in various cardiovascular pathologies. Ventilator-induced lung injury (VILI) is a life-threatening complication of mechanical ventilation at high tidal volumes associated with excessive mechanical stretch of pulmonary vascular endothelial cells. However, a role of VILI-relevant levels of cyclic stretch in microparticle generation by vascular endothelium remains unknown. We report microparticle formation by human pulmonary endothelial cells exposed to pathologic, but not physiologic, levels of mechanical stress. Stretch-induced microparticle generation was not affected by cell co-treatment with inflammatory agents thrombin or bacterial wall lipopolysacharide. Neither the basal nor the pathologic cyclic stretch-induced microparticle production was affected by Rho kinase and calpain inhibitors, but were instead abolished by caspase inhibitor. In contrast to lipopolysacharide, pathologic mechanical strain did not significantly induce apoptosis in pulmonary endothelial cells. These results show for the first time that mechanical strain of pulmonary endothelial cells at levels relevant to high tidal volume mechanical ventilation is a potent activator of microparticle formation, which requires caspase activity; however, this mechanism is independent of apoptosis. These results suggest a novel mechanism that may contribute to VILI-associated vascular dysfunction.

The expression of caspases is enhanced in peripheral blood mononuclear cells of autism spectrum disorder patients

Autism and autism spectrum disorders (ASDs) are heterogeneous complex neuro-developmental disorders characterized by dysfunctions in social interaction and communication skills. Their pathogenesis has been linked to interactions between genes and environmental factors. Consistent with the evidence of certain similarities between immune cells and neurons, autistic children also show an altered immune response of peripheral blood mononuclear cells (PBMCs). In this study, we investigated the activation of caspases, cysteinyl aspartate-specific proteases involved in apoptosis and several other cell functions in PBMCs from 15 ASD children compared to age-matched normal healthy developing controls. The mRNA levels for caspase-1, -2, -4, -5 were significantly increased in ASD children as compared to healthy subjects. Protein levels of Caspase-3, -7, -12 were also increased in ASD patients. Our data are suggestive of a possible role of the caspase pathway in ASD clinical outcome and of the use of caspase as potential diagnostic and/or therapeutic tools in ASD management.

Immunoreactivity of Ki-67/β-tubulin and immunocolocalization with active caspase-3 in rat dentate gyrus during postnatal development

This study was based on our previous report that the expression of active caspase-3 kept at a high level in dentate gyrus during postnatal development, which is not related to an apoptotic event. We addressed the hypothesis that the active caspase-3 expression may be related to a nonapoptotic role in the regulation of the cell cycle and differentiation or other physiological functions. To confirm this hypothesis, through a temporal investigation from postnatal day (P) 0, 4, 7, 10, 14, 21, 28, to 56, based on immunofluorescent method, we dual labeled active caspase-3 with Ki-67 or β-tubulin in the dentate gyrus. Our results showed a minority of active caspase-3 positive cells were colabeled with the proliferation marker Ki-67 in stratum moleculare (MOL), granular cell layer (GCL), subgranular zone (SGZ) and polymorphic stratum (POLY) from P0 to P14, and the colabeled cells decreased gradually with age. From P21 to P56, the colocalization of the two proteins was mainly focused on SGZ. There was a positive correlation between the positive cells of active caspase-3 with that of Ki-67. In addition, an extensive colocalization between active caspase-3 and β-tubulin was observed at all the age groups. There was a strong positive correlation between the intensity of active caspase-3 in GCL with that of β-tubulin in MOL, GCL and POLY of dentate gyrus and the stratum lucidum of CA3. Our data raised the possibility of a nonapoptotic role of active caspase-3 in dentate gyrus, which may be partly associated with cellular proliferation and differentiation, and also may be related to neurite outgrowth, axonal transport, or dendrite elongation of granular cells during postnatal development.

β-Catenin dynamics in the regulation of microvascular endothelial cell hyperpermeability

β-Catenin, a key regulator of barrier integrity, is an important component of the adherens junctional complex. Although the roles of β-catenin in maintaining the adherens junctions and Wnt signaling are known, the dynamics of β-catenin following insult and its potential role in vascular recovery/repair remain unclear. Our objective was to define β-catenin's dynamics following disruption of the adherens junctional complex and subsequent recovery. Rat lung microvascular endothelial cells were treated with active caspase 3 enzyme, by protein transference method, as an inducer of junctional damage and permeability. The disruption and subsequent recovery of β-catenin to the adherens junctions were studied via immunofluorescence. Rat lung microvascular endothelial cell monolayers were used to measure hyperpermeability. To understand the role of β-catenin on nuclear translocation/transcriptional regulation in relationship to the recovery of the adherens junctions, Tcf-mediated transcriptional activity was determined. Active caspase 3 induced a loss of β-catenin at the adherens junctions at 1 and 2 h followed by its recovery at 3 h. Transference of Bak peptide, an inducer of endogenous caspase 3 activation, induced hyperpermeability at 1 h followed by a significant decrease at 2 h. Inhibition of GSK-3β and the transfection of β-catenin vector increased Tcf-mediated transcription significantly (P < 0.05). The dissociated adherens junctional protein β-catenin translocates into the cytoplasm, resulting in microvascular hyperpermeability followed by a time-dependent recovery and relocation to the cell membrane. Our data suggest a recycling pathway for β-catenin to the cell junction.

Age-related intraneuronal elevation of αII-spectrin breakdown product SBDP120 in rodent forebrain accelerates in 3×Tg-AD mice

Spectrins line the intracellular surface of plasmalemma and play a critical role in supporting cytoskeletal stability and flexibility. Spectrins can be proteolytically degraded by calpains and caspases, yielding breakdown products (SBDPs) of various molecular sizes, with SBDP120 being largely derived from caspase-3 cleavage. SBDPs are putative biomarkers for traumatic brain injury. The levels of SBDPs also elevate in the brain during aging and perhaps in Alzheimer’s disease (AD), although the cellular basis for this change is currently unclear. Here we examined age-related SBDP120 alteration in forebrain neurons in rats and in the triple transgenic model of AD (3×Tg-AD) relative to non-transgenic controls. SBDP120 immunoreactivity (IR) was found in cortical neuronal somata in aged rats, and was prominent in the proximal dendrites of the olfactory bulb mitral cells. Western blot and densitometric analyses in wild-type mice revealed an age-related elevation of intraneuronal SBDP120 in the forebrain which was more robust in their 3×Tg-AD counterparts. The intraneuronal SBDP120 occurrence was not spatiotemporally correlated with transgenic amyloid precursor protein (APP) expression, β-amyloid plaque development, or phosphorylated tau expression over various forebrain regions or lamina. No microscopically detectable in situ activated caspase-3 was found in the nuclei of SBDP120-containing neurons. The present study demonstrates the age-dependent intraneuronal presence of an αII-spectrin cleavage fragment in mammalian forebrain which is exacerbated in a transgenic model of AD. This novel neuronal alteration indicates that impairments in membrane protein metabolism, possibly due to neuronal calcium mishandling and/or enhancement of calcium sensitive proteolysis, occur during aging and in transgenic AD mice.

Inflammasome-activated caspase 7 cleaves PARP1 to enhance the expression of a subset of NF-κB target genes

Caspase 1 is part of the inflammasome, which is assembled upon pathogen recognition, while caspases 3 and/or 7 are mediators of apoptotic and nonapoptotic functions. PARP1 cleavage is a hallmark of apoptosis yet not essential, suggesting it has another physiological role. Here we show that after LPS stimulation, caspase 7 is activated by caspase 1, translocates to the nucleus, and cleaves PARP1 at the promoters of a subset of NF-κB target genes negatively regulated by PARP1. Mutating the PARP1 cleavage site D214 renders PARP1 uncleavable and inhibits PARP1 release from chromatin and chromatin decondensation, thereby restraining the expression of cleavage-dependent NF-κB target genes. These findings propose an apoptosis-independent regulatory role for caspase 7-mediated PARP1 cleavage in proinflammatory gene expression and provide insight into inflammasome signaling.

CASP8 promoter polymorphism is associated with high-risk HPV types and abnormal cytology but not with cervical cancer

Only a small fraction of women infected with human papillomavirus (HPV) progress to cervical cancer pointing to additional risk factors including host genetics that might play a role in development of cervical cancer. Caspase-8 (encoded by CASP8 gene) is crucial in generating cell death signals to eliminate potentially malignant cells. Genetic variation in CASP8 might influence the susceptibility to cancer. CASP8 -652 6N ins/del polymorphism has been previously reported to influence the progression to several cancers including cervical cancer. This polymorphism was investigated in 445 women of black African and Mixed Ancestry origin with invasive cervical cancer and 1,221 controls matched (1:3) by age, ethnicity, and domicile status. Genotyping for CASP8 -652 6N ins/del was done by PCR-RFLP. In the control women cervical disease was detected by cervical cytology. The CASP8 -652 6N del/del genotype did not show any significant association (P=0.948) with cervical cancer. Further analysis within the controls showed a weak association (P=0.048) of this polymorphism with abnormal cytology in both ethnicities and high-risk HPV infection (P=0.030) only in the black Africans. This is the first study of the role of CASP8 -652 6N ins/del polymorphism in cervical cancer in an African population. These results show that CASP8 -652 6N del/del genotype increases the risk of abnormal cytology and high-risk HPV infection but does not show an association with cervical cancer. This result points towards an important role of CASP8 in HPV infection and in the development of pre-cancers.

Naturally occurring triggers that induce apoptosis-like programmed cell death in Plasmodium berghei ookinetes

Several protozoan parasites have been shown to undergo a form of programmed cell death that exhibits morphological features associated with metazoan apoptosis. These include the rodent malaria parasite, Plasmodium berghei. Malaria zygotes develop in the mosquito midgut lumen, forming motile ookinetes. Up to 50% of these exhibit phenotypic markers of apoptosis; as do those grown in culture. We hypothesised that naturally occurring signals induce many ookinetes to undergo apoptosis before midgut traversal. To determine whether nitric oxide and reactive oxygen species act as such triggers, ookinetes were cultured with donors of these molecules. Exposure to the nitric oxide donor SNP induced a significant increase in ookinetes with condensed nuclear chromatin, activated caspase-like molecules and translocation of phosphatidylserine that was dose and time related. Results from an assay that detects the potential-dependent accumulation of aggregates of JC-1 in mitochondria suggested that nitric oxide does not operate via loss of mitochondrial membrane potential. L-DOPA (reactive oxygen species donor) also caused apoptosis in a dose and time dependent manner. Removal of white blood cells significantly decreased ookinetes exhibiting a marker of apoptosis in vitro. Inhibition of the activity of nitric oxide synthase in the mosquito midgut epithelium using L-NAME significantly decreased the proportion of apoptotic ookinetes and increased the number of oocysts that developed. Introduction of a nitric oxide donor into the blood meal had no effect on mosquito longevity but did reduce prevalence and intensity of infection. Thus, nitric oxide and reactive oxygen species are triggers of apoptosis in Plasmodium ookinetes. They occur naturally in the mosquito midgut lumen, sourced from infected blood and mosquito tissue. Up regulation of mosquito nitric oxide synthase activity has potential as a transmission blocking strategy.

PP2A:B56{epsilon}, a substrate of caspase-3, regulates p53-dependent and p53-independent apoptosis during development

Protein phosphatase 2A (PP2A) is one of the most abundantly expressed serine/threonine protein phosphatases. A large body of evidence suggests that PP2A is a tumor suppressor and plays critical roles in regulating apoptosis. PP2A is a heterotrimeric protein complex. Its substrate specificity, localization, and activity are regulated by regulatory subunits of PP2A. A recent study has demonstrated that single nucleotide polymorphism in B56ε (PPP2R5E), a B56 family regulatory subunit of PP2A, is associated with human soft tissue sarcoma. This raises the possibility that B56ε is involved in tumorigenesis and plays important roles in regulating apoptosis. However, this hypothesis has not been tested experimentally. Our previous studies revealed that B56ε regulates a number of developmental signaling pathways during early embryonic patterning. Here we report novel functions of B56ε in regulating apoptosis. We provide evidence that B56ε has both anti- and pro-apoptotic functions. B56ε suppresses p53-independent apoptosis during neural development, but triggers p53-dependent apoptosis. Mechanistically, B56ε regulates the p53-dependent apoptotic pathway solely through controlling the stability of p53 protein. In addition to its function in regulating apoptosis, we show that B56ε undergoes proteolytic cleavage. The cleavage of B56ε is mediated by caspase-3 and occurs on the carboxyl side of an evolutionarily conserved N-terminal "DKXD" motif. These results demonstrate that B56ε, a substrate of caspase-3, is an essential regulator of apoptosis. So far, we have identified an alternative translation isoform and a caspase cleavage product of B56ε. The significance of post-transcriptional regulation of B56ε is discussed.

A multi-factor model for caspase degradome prediction

BACKGROUND

Caspases belong to a class of cysteine proteases which function as critical effectors in cellular processes such as apoptosis and inflammation by cleaving substrates immediately after unique tetrapeptide sites. With hundreds of reported substrates and many more expected to be discovered, the elucidation of the caspase degradome will be an important milestone in the study of these proteases in human health and disease. Several computational methods for predicting caspase cleavage sites have been developed recently for identifying potential substrates. However, as most of these methods are based primarily on the detection of the tetrapeptide cleavage sites - a factor necessary but not sufficient for predicting in vivo substrate cleavage - prediction outcomes will inevitably include many false positives.

RESULTS

In this paper, we show that structural factors such as the presence of disorder and solvent exposure in the vicinity of the cleavage site are important and can be used to enhance results from cleavage site prediction. We constructed a two-step model incorporating cleavage site prediction and these factors to predict caspase substrates. Sequences are first predicted for cleavage sites using CASVM or GraBCas. Predicted cleavage sites are then scored, ranked and filtered against a cut-off based on their propensities for locating in disordered and solvent exposed regions. Using an independent dataset of caspase substrates, the model was shown to achieve greater positive predictive values compared to CASVM or GraBCas alone, and was able to reduce the false positives pool by up to 13% and 53% respectively while retaining all true positives. We applied our prediction model on the family of receptor tyrosine kinases (RTKs) and highlighted several members as potential caspase targets. The results suggest that RTKs may be generally regulated by caspase cleavage and in some cases, promote the induction of apoptotic cell death - a function distinct from their role as transducers of survival and growth signals.

CONCLUSION

As a step towards the prediction of in vivo caspase substrates, we have developed an accurate method incorporating cleavage site prediction and structural factors. The multi-factor model augments existing methods and complements experimental efforts to define the caspase degradome on the systems-wide basis.

Extremely low frequency (ELF) magnetic fields and apoptosis: a review

In recent years, there has been increasing evidence that extremely low frequency magnetic fields might be linked to tumours, particularly with childhood leukaemia. In the same period, the role of apoptosis in the tumour process has also gained increasing importance. It is the purpose of this review to describe the apoptotic process, discuss selected papers in which apoptosis is examined in cells exposed to magnetic fields and describe the possible biophysical mechanisms responsible for changes in the apoptotic process in exposed cells. Despite some differences, as a whole, the literature seems to demonstrate that magnetic fields induce changes in apoptosis in cells exposed to different experimental protocols. In addition, the important role of ions, particularly of Ca2+, in the apoptotic process is also discussed, and one possible model for magnetic field action on apoptosis that brings together experimental observations of different nature is suggested and discussed.

Critical role for caspase-8 in epidermal growth factor signaling

Caspase-8 has a well-defined canonical role as an apical protease of the extrinsic apoptosis pathway. Evidence is growing, however, that the protein has numerous other nonapoptotic functions. We have previously shown that caspase-8 is required for efficient adhesion-induced activation of the extracellular signal-regulated kinase (Erk)-1/2 pathway. We now show that caspase-8 is also necessary for the efficient activation of downstream events associated with epidermal growth factor (EGF) signaling. This promotion of EGF-induced Erk1/2 activation is independent of the proteolytic activity of caspase-8 and can be recapitulated using only the pro-domains of the protein. In addition, we identify specific residues within the caspase-8 "RXDLL motif" that are essential for Erk pathway activation. Furthermore, these residues are also involved in forming a complex with the tyrosine kinase Src. Caspase-8 null cells and cells reconstituted with caspase-8 harboring point mutations of these critical amino acids also show defective EGF-induced migration as compared with cells reconstituted with the wild-type protein. In sum, we provide the first evidence for caspase-8 as an essential component of growth factor signaling and suggest that this may be due to its association with Src. As the EGF/Src pathway activity has been shown to promote oncogenic events, our findings that caspase-8 is necessary for these activities may help explain why it is rarely deleted or silenced in tumors.

Different ways to die: cell death modes of the unicellular chlorophyte Dunaliella viridis exposed to various environmental stresses are mediated by the caspase-like activity DEVDase

Programmed cell death is necessary for homeostasis in multicellular organisms and it is also widely recognized to occur in unicellular organisms. However, the mechanisms through which it occurs in unicells, and the enzymes involved within the final response is still the subject of heated debate. It is shown here that exposure of the unicellular microalga Dunaliella viridis to several environmental stresses, induced different cell death morphotypes, depending on the stimulus received. Senescent cells demonstrated classical and unambiguous apoptotic-like characteristics such as chromatin condensation, DNA fragmentation, intact organelles, and blebbing of the cell membrane. Acute heat shock caused general swelling and altered plasma membrane, but the presence of chromatin clusters and DNA strand breaks suggested a necrotic-like event. UV irradiated cells presented changes typical for necrosis, together with apoptotic characteristics resembling an intermediate cell-death phenotype termed aponecrosis-like. Cells subjected to hyperosmotic shock revealed chromatin spotting without DNA fragmentation, and extensive cytoplasmic swelling and vacuolization, comparable to a paraptotic-like cell death phenotype. Nitrogen-starved cells showed pyknosis, blebbing, and cytoplasmic consumption, indicating a similarity to autophagic/vacuolar-like cell death. The caspase-like activity DEVDase was measured by using the fluorescent substrate Ac-DEVD-AMC and antibodies against the human caspase-3 active enzyme cross-reacted with bands, the intensity of which paralleled the activity. All the environmental stresses tested produced a substantial increase in both DEVDase activity and protein levels. The irreversible caspase-3 inhibitor Z-DEVD-FMK completely inhibited the enzymatic activity whereas serine and aspartyl proteases inhibitors did not. These results show that cell death in D. viridis does not conform to a single pattern and that environmental stimuli may produce different types of cell death depending on the type and intensity of the stimulus, all of which help to understand the cell death-dependent and cell death-independent functions of caspase-like proteins. Hence, these data support the theory that alternative, non-apoptotic programmed cell death (PCDs), exist either in parallel or in an independent manner with apoptosis and were already present in single-celled organisms that evolved some 1.2-1.6 billion years ago.

Caspase-2(L), caspase-9, and caspase-3 during in vitro maturation and fragmentation of the mouse oocyte

Several studies have shown that apoptotic pathways control fragmentation of unfertilized ovulated oocyte, induced by doxorubicin. But very few have investigated the basis of this process, from prophase I to later stages. Our results revealed the presence of caspase-2(L), caspase-9, and caspase-3 in their zymogen and cleaved forms in the oocyte before meiosis resumption. Caspase-2(L) and caspase-9 were detected in the nucleus of GV-oocytes in a distribution related to chromatin configuration. The inhibition of caspase activity by Z-VAD-fmk accelerated the transition from metaphase I to metaphase II, and caspase-9 and caspase-3 were detected along the meiotic spindle. Surprisingly, Western blot analysis revealed that the three cleaved caspases were present in similar amounts in healthy and fragmented oocytes and caspase inhibition did not prevent doxorubicin-induced apoptosis. Our results suggest that, if cleaved, caspases may be dispensable for final oocyte death and they could be involved in regulating the maturation process.

Targeted cleavage of signaling proteins by caspase 3 inhibits T cell receptor signaling in anergic T cells

T cell receptor (TCR) engagement in the absence of costimulation induces the calcium-dependent upregulation of a program of gene expression that leads to the establishment of T cell anergy. Casp3 is one of the genes activated during anergy induction. Here we show that caspase 3 is required for the induction of T cell unresponsiveness. Suboptimal T cell stimulation induced caspase 3 activation, which did not result in cell death. Furthermore, caspase 3-deficient T cells showed impaired responses to anergizing stimuli. In anergic T cells, activated caspase 3 associated to the plasma membrane, where it cleaved and inactivated proteins such as the Grb2-related adaptor downstream of shc (GADS) and the guanine-nucleotide exchange factor Vav1, causing a blockade in TCR signaling. Our results identify a role for caspase 3 in nonapoptotic T cells and support that caspase 3-dependent proteolytic inactivation of signaling proteins is essential to maintain T cell tolerance.

Alternative processing of sterol regulatory element binding protein during larval development in Drosophila melanogaster

Sterol regulatory element binding protein (SREBP) is a major transcriptional regulator of lipid metabolism. Nuclear Drosophila SREBP (dSREBP) is essential for larval development in Drosophila melanogaster but dispensable in adults. dSREBP(-) larvae die at second instar owing to loss of dSREBP-mediated transcription but survive to adulthood when fed fatty acids. Activation of SREBP requires two separate cleavages. Site-1 protease (S1P) cleaves in the luminal loop of the membrane-bound SREBP precursor, cutting it in two. The NH(2)- and COOH-terminal domains remain membrane bound owing to their single membrane-spanning helices. The NH(2)-terminal cleavage product is the substrate for site-2 protease (S2P), which cleaves within its membrane-spanning helix to release the transcription factor. In mice, loss of S1P is lethal but the consequences of loss of S2P in animals remain undefined. All known functions of SREBP require its cleavage by S2P. We isolated Drosophila mutants that eliminate all dS2P function (dS2P(-)). Unexpectedly, larvae lacking dS2P are viable. They are deficient in transcription of some dSREBP target genes but less so than larvae lacking dSREBP. Despite loss of dS2P, dSREBP is processed in mutant larvae. Therefore, larvae have an alternative cleavage mechanism for producing transcriptionally active dSREBP, and this permits survival of dS2P mutants.

MicroRNAs: key players in the immune system, differentiation, tumorigenesis and cell death

Micro (mi)RNAs are small, highly conserved noncoding RNAs that control gene expression post-transcriptionally either via the degradation of target mRNAs or the inhibition of protein translation. Each miRNA is believed to regulate the expression of multiple mRNA targets, and many miRNAs have been linked to the initiation and progression of human cancer. miRNAs control various activities of the immune system and different stages of hematopoietic development, and their misexpression is the cause of various blood malignancies. Certain miRNAs have oncogenic activities, whereas others have the potential to act as tumor suppressors. Because they control fundamental processes such as differentiation, cell growth and cell death, the study of the role of miRNAs in human neoplasms holds great promise for novel forms of therapy. Here, we summarize the role of miRNAs and their targets in contributing to human cancers and their function as regulators of apoptotic pathways and the immune system.

Pro- and anti-apoptotic roles for IGF-I in TNF-alpha-induced apoptosis: a MAP kinase mediated mechanism

OBJECTIVE

The concept of skeletal muscle homeostasis--often viewed as the net balance between two separate processes, namely protein degradation and protein synthesis--are not occurring independently of each other, but are finely co-ordinated by a web of intricate signalling networks.

MATERIALS AND METHODS

Using rodent muscle cell lines we have investigated TNF-alpha/IGF-I interactions, in an attempt to mimic and understand mechanisms underlying the wasting process.

RESULTS AND CONCLUSION

When myoblast cells are incubated with TNF-alpha (10 ng ml(- 1)) maximal damage ( approximately 21% +/- 0.7 myoblast death, p < 0.05) was induced. Co-incubation of TNF-alpha (10 ng ml(- 1)) with IGF-I resulted in cell survival ( approximately 50% reduction in myoblast death, p < 0.05), however, myotube formation was not evident. In contrast, a novel role of IGF-I has been identified whereby co-incubation of muscle cells with IGF-I (1.5 ng ml(- 1)) and a non-apoptotic dose of TNF-alpha (1.25 ng ml(- 1); sufficient to block differentiation) unexpectedly were shown not to rescue a block on differentiation but to facilitate significant myoblast death (p < 0.05). Interestingly, pre-administration of PD98059, a MAPK signal-blocking agent followed by co-incubation of 1.25 ng ml(- 1) TNF-alpha and 1.5 ng ml(- 1) IGF-I, reduced death to baseline levels (p < 0.05). We show for the first time that IGF-I can be apoptotic in the absence of TNF-alpha-induced cell death.

Apoptotic caspase activation and activity

Caspases are central to the execution of apoptosis. Their proteolytic activity is responsible for the demise of cells in many physiological and pathological states. Great advances in understanding caspases have been made using recombinant caspase expression and enzymatic characterization. Assays to measure caspase activity in apoptotic cell extracts and the development of a reconstituted cell-free assay were also critical in establishing the hierarchy in the caspase activation cascade and comprehend how caspase-9 is activated by the apoptosome. More recently, new tools such as activity-based probes allowed us to detect caspase activation in their working environment providing readout of the system with minimal interference. This chapter describes some of the methods used by our group to study the activation mechanisms of caspases and their activity.

Human papillomaviruses activate caspases upon epithelial differentiation to induce viral genome amplification

The life cycle of human papillomaviruses (HPVs) is linked to epithelial differentiation, with late viral events restricted to the uppermost stratified layers. Our studies indicated that HPV activates capases-3, -7, and -9 upon differentiation, whereas minimal activation was observed in differentiating normal keratinocytes. Activation occurred in the absence of significant levels of apoptosis, suggesting a potential role for caspases in the viral life cycle. In support of this, the addition of caspase inhibitors significantly impaired differentiation-dependent viral genome amplification. A conserved caspase cleavage motif was identified in the replication protein E1 ((46)DxxD(49)) that was targeted in vitro by both recombinant caspase-3 and caspase-7. Mutation of this site inhibited amplification of viral genomes, indicating that caspase cleavage is necessary for the productive viral life cycle. Our study demonstrates that HPV activates caspases upon differentiation to facilitate productive viral replication and represents a way by which HPV controls viral gene function in differentiating cells.

CASVM: web server for SVM-based prediction of caspase substrates cleavage sites

Caspases belong to a unique class of cysteine proteases which function as critical effectors of apoptosis, inflammation and other important cellular processes. Caspases cleave substrates at specific tetrapeptide sites after a highly conserved aspartic acid residue. Prediction of such cleavage sites will complement structural and functional studies on substrates cleavage as well as discovery of new substrates. We have recently developed a support vector machines (SVM) method to address this issue. Our algorithm achieved an accuracy ranging from 81.25 to 97.92%, making it one of the best methods currently available. CASVM is the web server implementation of our SVM algorithms, written in Perl and hosted on a Linux platform. The server can be used for predicting non-canonical caspase substrate cleavage sites. We have also included a relational database containing experimentally verified caspase substrates retrievable using accession IDs, keywords or sequence similarity.

AVAILABILITY

http://www.casbase.org/casvm/index.html