Cascades of mammalian caspase activation in the yeast Saccharomyces cerevisiae

Heterologous Expression and Auto-Activation of Human Pro-Inflammatory Caspase-1 in Saccharomyces cerevisiae and Comparison to Caspase-8

Caspases are a family of cysteine proteases that play an essential role in inflammation, apoptosis, cell death, and development. Here we delve into the effects caused by heterologous expression of human caspase-1 in the yeast Saccharomyces cerevisiae and compare them to those of caspase-8. Overexpression of both caspases in the heterologous model led to their activation and caused mitochondrial hyperpolarization, damage to different organelles, and cell death. All these effects were dependent on their protease activity, and caspase-8 was more aggressive than caspase-1. Growth arrest could be at least partially explained by dysfunction of the actin cytoskeleton as a consequence of the processing of the yeast Bni1 formin, which we identify here as a likely direct substrate of both caspases. Through the modulation of the GAL1 promoter by using different galactose:glucose ratios in the culture medium, we have established a scenario in which caspase-1 is sufficiently expressed to become activated while yeast growth is not impaired. Finally, we used the yeast model to explore the role of death-fold domains (DD) of both caspases in their activity. Peculiarly, the DDs of either caspase showed an opposite involvement in its intrinsic activity, as the deletion of the caspase activation and recruitment domain (CARD) of caspase-1 enhanced its activity, whereas the deletion of the death effector domain (DED) of caspase-8 diminished it. We show that caspase-1 is able to efficiently process its target gasdermin D (GSDMD) when co-expressed in yeast. In sum, we propose that S. cerevisiae provides a manageable tool to explore caspase-1 activity and structure–function relationships.

Lactoferrin and Its Derived Peptides: An Alternative for Combating Virulence Mechanisms Developed by Pathogens

Due to the emergence of multidrug-resistant pathogens, it is necessary to develop options to fight infections caused by these agents. Lactoferrin (Lf) is a cationic nonheme multifunctional glycoprotein of the innate immune system of mammals that provides numerous benefits. Lf is bacteriostatic and/or bactericidal, can stimulate cell proliferation and differentiation, facilitate iron absorption, improve neural development and cognition, promote bone growth, prevent cancer and exert anti-inflammatory and immunoregulatory effects. Lactoferrin is present in colostrum and milk and is also produced by the secondary granules of polymorphonuclear leukocytes, which store this glycoprotein and release it at sites of infection. Lf is also present in many fluids and exocrine secretions, on the surfaces of the digestive, respiratory and reproductive systems that are commonly exposed to pathogens. Apo-Lf (an iron-free molecule) can be microbiostatic due to its ability to capture ferric iron, blocking the availability of host iron to pathogens. However, apo-Lf is mostly microbicidal via its interaction with the microbial surface, causing membrane damage and altering its permeability function. Lf can inhibit viral entry by binding to cell receptors or viral particles. Lf is also able to counter different important mechanisms evolved by microbial pathogens to infect and invade the host, such as adherence, colonization, invasion, production of biofilms and production of virulence factors such as proteases and toxins. Lf can also cause mitochondrial and caspase-dependent regulated cell death and apoptosis-like in pathogenic yeasts. All of these mechanisms are important targets for treatment with Lf. Holo-Lf (the iron-saturated molecule) can contain up to two ferric ions and can also be microbicidal against some pathogens. On the other hand, lactoferricins (Lfcins) are peptides derived from the N-terminus of Lf that are produced by proteolysis with pepsin under acidic conditions, and they cause similar effects on pathogens to those caused by the parental Lf. Synthetic analog peptides comprising the N-terminus Lf region similarly exhibit potent antimicrobial properties. Importantly, there are no reported pathogens that are resistant to Lf and Lfcins; in addition, Lf and Lfcins have shown a synergistic effect with antimicrobial and antiviral drugs. Due to the Lf properties being microbiostatic, microbicidal, anti-inflammatory and an immune modulator, it represents an excellent natural alternative either alone or as adjuvant in the combat to antibiotic multidrug-resistant bacteria and other pathogens. This review aimed to evaluate the data that appeared in the literature about the effects of Lf and its derived peptides on pathogenic bacteria, protozoa, fungi and viruses and how Lf and Lfcins inhibit the mechanisms developed by these pathogens to cause disease.

Overexpression and cytoplasmic localization of caspase-6 is associated with lamin A degradation in set of ovarian cancers

Background

In most women with ovarian cancer, the diagnosis occurs after dissemination of tumor cells beyond ovaries. Several molecular perturbations occur ahead of tumor initiation including loss of lamin A/C. Our hypothesis was that the loss of nuclear structural proteins A type lamins (lamin A/C) transcribed from LMNA gene and substrate for active caspase-6 maybe one of the molecular perturbations. Our objective is to investigate the association between the loss of lamin A/C and the overexpression of caspase-6 in ovarian cancer cells.

Method

Western blotting and immunofluorescence were used to analyze the expression of lamin A/C and active caspase-6 in normal human ovarian surface epithelial (HOSE) cells, immortalized human ovarian surface epithelial cells and a set of seven ovarian cancer cell lines (including OVCAR3, OVCAR5, and A2780). The activity of caspase-6 was measured by densitometry, fluorescence and flow cytometry. Immunohistochemistry was used to evaluate the expression of caspase-6 in set of ovarian cancer tissues previously reported to have lost lamin A/C.

Results

The results showed that HOSE cells expressed lamin A/C and no or low level of active caspase-6 while cancer cells highly expressed caspase-6 and no or low level of lamin A/C. The inhibition of caspase-6 activity in OVCAR3 cells increased lamin A but has no effect on lamin C; active caspase-6 was localized in the cytoplasm associated with the loss of lamin A.

Conclusion

Overexpression and cytoplasmic localization of caspase-6 in ovarian cancer cells may be involved in lamin A degradation and deficiency observed in some ovarian cancer cells.

The Yeast Saccharomyces cerevisiae as a Model for Understanding RAS Proteins and their Role in Human Tumorigenesis

The exploitation of the yeast Saccharomyces cerevisiae as a biological model for the investigation of complex molecular processes conserved in multicellular organisms, such as humans, has allowed fundamental biological discoveries. When comparing yeast and human proteins, it is clear that both amino acid sequences and protein functions are often very well conserved. One example of the high degree of conservation between human and yeast proteins is highlighted by the members of the RAS family. Indeed, the study of the signaling pathways regulated by RAS in yeast cells led to the discovery of properties that were often found interchangeable with RAS proto-oncogenes in human pathways, and vice versa. In this work, we performed an updated critical literature review on human and yeast RAS pathways, specifically highlighting the similarities and differences between them. Moreover, we emphasized the contribution of studying yeast RAS pathways for the understanding of human RAS and how this model organism can contribute to unveil the roles of RAS oncoproteins in the regulation of mechanisms important in the tumorigenic process, like autophagy.

Monocrotaline: histological damage and oxidant activity in brain areas of mice

This work was designed to study MCT effect in histopathological analysis of hippocampus (HC) and parahippocampal cortex (PHC) and in oxidative stress (OS) parameters in brain areas such as hippocampus (HC), prefrontal cortex (PFC), and striatum (ST). Swiss mice (25–30 g) were administered a single i.p. dose of MCT (5, 50, or 100 mg/kg) or 4% Tween 80 in saline (control group). After 30 minutes, the animals were sacrificed by decapitation and the brain areas (HC, PHC, PFC, or ST) were removed for histopathological analysis or dissected and homogenized for measurement of OS parameters (lipid peroxidation, nitrite, and catalase) by spectrophotometry. Histological evaluation of brain structures of rats treated with MCT (50 and 100 mg/kg) revealed lesions in the hippocampus and parahippocampal cortex compared to control. Lipid peroxidation was evident in all brain areas after administration of MCT. Nitrite/nitrate content decreased in all doses administered in HC, PFC, and ST. Catalase activity was increased in the MCT group only in HC. In conclusion, monocrotaline caused cell lesions in the hippocampus and parahippocampal cortex regions and produced oxidative stress in the HC, PFC, and ST in mice. These findings may contribute to the neurological effects associated with this compound.

New insights into cancer-related proteins provided by the yeast model

Cancer is a devastating disease with a profound impact on society. In recent years, yeast has provided a valuable contribution with respect to uncovering the molecular mechanisms underlying this disease, allowing the identification of new targets and novel therapeutic opportunities. Indeed, several attributes make yeast an ideal model system for the study of human diseases. It combines a high level of conservation between its cellular processes and those of mammalian cells, with advantages such as a short generation time, ease of genetic manipulation and a wealth of experimental tools for genome- and proteome-wide analyses. Additionally, the heterologous expression of disease-causing proteins in yeast has been successfully used to gain an understanding of the functions of these proteins and also to provide clues about the mechanisms of disease progression. Yeast research performed in recent years has demonstrated the tremendous potential of this model system, especially with the validation of findings obtained with yeast in more physiologically relevant models. The present review covers the major aspects of the most recent developments in the yeast research area with respect to cancer. It summarizes our current knowledge on yeast as a cellular model for investigating the molecular mechanisms of action of the major cancer-related proteins that, even without yeast orthologues, still recapitulate in yeast some of the key aspects of this cellular pathology. Moreover, the most recent contributions of yeast genetics and high-throughput screening technologies that aim to identify some of the potential causes underpinning this disorder, as well as discover new therapeutic agents, are discussed.

Familial amyloid precursor protein mutants cause caspase-6-dependent but amyloid β-peptide-independent neuronal degeneration in primary human neuron cultures

Although familial Alzheimer disease (AD)-associated autosomal dominant mutants have been extensively studied, little is known about the underlying molecular mechanisms of neurodegeneration induced by these mutants in AD. Wild-type, Swedish or London amyloid precursor protein (APP) transfection in primary human neurons induced neuritic beading, in which several co-expressed proteins, such as enhanced green fluorescent protein, red fluorescent protein (RFP)-tau and RFP-ubiquitin, accumulated. APP-induced neuritic beading was dependent on caspase-6 (Casp6), because it was inhibited with 5 μM z-VEID-fmk or with dominant-negative Casp6. Neuritic beading was independent from APP-mediated amyloid β-peptide (Aβ) production, because the APPM596V (APP(MV)) mutant, which cannot generate Aβ, still induced Casp6-dependent neuritic beading. However, the beaded neurons underwent Casp6- and Aβ-dependent cell death. These results indicate that overexpression of wild-type or mutant APP causes Casp6-dependent but Aβ-independent neuritic degeneration in human neurons. Because Casp6 is activated early in AD and is involved in axonal degeneration, these results suggest that the inhibition of Casp6 may represent an efficient early intervention against familial forms of AD. Furthermore, these results indicate that removing Aβ without inhibiting Casp6 may have little effect in preventing the progressive dementia associated with sporadic or familial AD.

Identification and characterization of GRIM-1, a cell-death-associated gene product

Using a genome-wide technical knockout, we isolated a newly identified set of GRIM (genes associated with retinoid-interferon-induced mortality) genes; GRIM genes mediate IFN- and retinoic-acid (RA)-induced cell death. Here, we describe the isolation and characterization of one such gene, GRIM-1. Three proteins, with identical C-termini, were produced from the GRIM-1 open reading frame when this gene was transcribed and translated in vitro. These protein isoforms, designated GRIM-1alpha, GRIM-1beta and GRIM-1gamma, differentially suppressed growth via apoptosis in various cell lines. We also show that a caspase-dependent mechanism generates the proapoptotic GRIM-1 isoforms. Lastly, GRIM-1 isoforms differentially blocked maturation of 18S ribosomal RNA, consistent with their respective growth-suppressive ability. Together, these studies identified a novel protein involved in growth suppression and cell death.

Role of individual caspases induced by astrovirus on the processing of its structural protein and its release from the cell through a non-lytic mechanism

Caspases (Casp) activity has been associated with the intracellular proteolytic processing of the structural protein to yield the mature capsid formed by VP70 and with the cell release of human astrovirus (HAstV). This work describes the role of individual Casp on these events. The activity of initiator (-8, -9) and executioner (-3/7) Casp was clearly detected at 12h post-infection. All these proteases were able to cleave VP90 in an in vitro assay, but this processing was blocked in cells transfected with siRNA against Casp-3, -9, but not against Casp-8. In contrast, virus release, observed in the absence of cell lysis, was more drastically affected by either silencing Casp-3 or in the presence of the inhibitor Ac-DEVD-CHO. Cleavage of VP90 to yield VP70 was mapped at motif TYVD(657). These data indicate that the processing of VP90 and the release of HAstV from the cell are two Casp-related, but apparently independent, events.

Immunohistochemical expression of caspase-1 and -9, uncleaved caspase-3 and -6, cleaved caspase-3 and -6 as well as Bcl-2 in benign epithelium and cancer of the prostate

Activation of caspases is an essential prerequisite for induction of apoptosis. In many tumors caspases are down-regulated, while anti-apoptotic Bcl-2 is up-regulated. To elucidate their putative role in prostate cancer (PCa) we determined the expression of different caspases and Bcl-2 in benign prostate epithelium (BPE) and PCa. Paraffin-embedded prostate whole mounts were cut (4 μm) and investigated immunohistochemically using monoclonal antibodies against caspase-1 and -9, uncleaved caspase-3 and -6, cleaved caspase-3 and -6, and Bcl-2. In BPE all caspases were localized to the cytoplasm of glandular cells. In PCa we found a statistically significant reduction in cleaved caspase-3 and -6 compared to the levels in BPE. The Bcl-2 protein was detected in the basal compartment of epithelial gland cells, but no immunostaining was noted in PCa. The decreased immunoreactivity of activated caspases probably indicates an alteration in post-translational cleavage that may play an important role during PCa progression.

Versatile assays for high throughput screening for activators or inhibitors of intracellular proteases and their cellular regulators

BACKGROUND

Intracellular proteases constitute a class of promising drug discovery targets. Methods for high throughput screening against these targets are generally limited to in vitro biochemical assays that can suffer many technical limitations, as well as failing to capture the biological context of proteases within the cellular pathways that lead to their activation. METHODS #ENTITYSTARTX00026;

FINDINGS

We describe here a versatile system for reconstituting protease activation networks in yeast and assaying the activity of these pathways using a cleavable transcription factor substrate in conjunction with reporter gene read-outs. The utility of these versatile assay components and their application for screening strategies was validated for all ten human Caspases, a family of intracellular proteases involved in cell death and inflammation, including implementation of assays for high throughput screening (HTS) of chemical libraries and functional screening of cDNA libraries. The versatility of the technology was also demonstrated for human autophagins, cysteine proteases involved in autophagy.

CONCLUSIONS

Altogether, the yeast-based systems described here for monitoring activity of ectopically expressed mammalian proteases provide a fascile platform for functional genomics and chemical library screening.

Human initiator caspases trigger apoptotic and autophagic phenotypes in Saccharomyces cerevisiae

Caspases are a family of proteases that participate in the progression and execution of the apoptotic program. However, regulation of the caspase activation and their substrates has not yet been fully elucidated. Here we explore the effect of the ectopic expression of the human initiator caspases-8 and -10 in Saccharomyces cerevisiae. Our results showed that the expression of human CASP10 and CASP8 triggers certain apoptotic markers such as a massive production of reactive oxygen species (ROS), chromatin condensation and phosphatidylserine externalization, finally leading to cell death. In response to hydroxyurea (HU), yeast cells expressing caspase-10 did not reduce the replication of DNA and escaped to the intra-S checkpoint of the cell cycle. In addition, caspase-10 expression induced yeast vacuolization and a vacuole-associated phenotype resembling autophagy. Other intracellular alterations such as disorganization of the actin cytoskeleton, cell wall damage, and aberrations within the endoplasmic reticulum lumen were also associated with caspase-10 expression. Furthermore, caspase-induced cell death was completely dependent on the proteolytic activation of the enzyme but, in contrast, was not dependent on either of the endogenous yeast apoptotic proteins Aif1 and Mca1 or the mitochondria.

Self-activation of Caspase-6 in vitro and in vivo: Caspase-6 activation does not induce cell death in HEK293T cells

Caspase-6 (Casp6) is a short pro-domain caspase that is activated early in Alzheimer disease, yet, little is known on the mechanism of activation of this caspase. In this study, critical proteolytic processing events required for Casp6 activation in vitro and in vivo were evaluated by site directed mutagenesis of the D23 pro-domain, and D179 and D193 linker processing sites. We found that (1) Casp6 was self-processed and activated in vitro and in vivo, (2) uncleavable Casp6 possessed low activity in vitro but not in vivo, (3) the pro-domain of Casp6 entirely prevented self-processing and activation in vivo but not in vitro, (4) removal of the pro-domain promoted Casp6 activation, (5) cleavage at either D179 or D193 was sufficient to generate activity in vitro and in vivo, and (6) Casp6 activity did not induce cell death in HEK293T cells. We conclude that the Casp6 is activated through proteolytic cleavage, as are the effector Caspase-3 and -7. However, unlike other effector caspases, Casp6 can be entirely self-activated and its activation does not necessarily induce cell death.

Caspase-dependent apoptosis in yeast

Damaging environment, certain intracellular defects or heterologous expression of pro-apoptotic genes induce death in yeast cells exhibiting typical markers of apoptosis. In mammals, apoptosis can be directed by the activation of groups of proteases, called caspases, that cleave specific substrates and trigger cell death. In addition, in plants, fungi, Dictyostelium and metazoa, paracaspases and metacaspases have been identified that share some homologies with caspases but showing different substrate specificity. In the yeast Saccharomyces cerevisiae, a gene (MCA1/YCA1) has been identified coding for a metacaspase involved in the induction of cell death. Metacaspases are not biochemical, but sequence and functional homologes of caspases, as deletion of them rescues entirely different death scenarios. In this review we will summarize the current knowledge in S. cerevisiae on apoptotic processes, induced by internal and external triggers, which are dependent on the metacaspase gene YCA1.

X-linked inhibitor of apoptosis protein as a therapeutic target

Dysregulation of apoptosis has been shown to contribute to many diseases, including cancer formation, development and resistance, as well as neurodegenerative and autoimmune disorders. One mechanism through which tumour cells are believed to acquire resistance to apoptosis is by overexpression of X-linked inhibitor of apoptosis protein (XIAP), which belongs to a family of inhibitor of apoptosis proteins. When XIAP is overexpressed, cancer cells are rendered resistant to apoptosis, both intrinsically and in response to chemotherapy and radiotherapy. Significant progress has been made in targeting XIAP therapeutically, both directly and indirectly through the modulation of other molecules involved in the apoptotic pathway. This review introduces XIAP from its molecular origins, discusses its modulation and potential as a novel drug target, and considers future therapeutic perspectives.

Engineered apoptotic nucleases for chromatin research

We have created new genomics tools for chromatin research by genetically engineering the human and mouse major apoptotic nucleases that are responsible for internucleosomal DNA cleavage, DNA fragmentation factor (DFF). Normally, in its inactive form, DFF is a heterodimer composed of a 45-kDa chaperone inhibitor subunit (DFF45 or ICAD), and a 40-kDa latent endonuclease subunit (DFF40 or CAD). Upon caspase-3 cleavage of DFF45, DFF40 forms active endonuclease homo-oligomers. Although Saccharomyces cerevisiae lacks DFF, expression of caspase-3 is lethal in this organism, but expression of the highly sequence-specific tobacco etch virus protease (TEVP) is harmless. Therefore, we inserted TEVP cleavage sites immediately downstream of the two caspase-3 cleavage sites within DFF45, generating a novel form of DFF (DFF-T) whose nuclease activity proved to be exclusively under the control of TEVP. We demonstrate that co-expression of TEVP and DFF-T under galactose control results in nucleosomal DNA laddering and cell death in S. cerevisiae. We also created synthetic DFF genes with optimized codons for high-level expression in Eschericia coli or S. cerevisiae. We further demonstrate the excellence of the synthetic gene products for in vitro mapping of the nucleosome positions and hypersensitive sites in specific genes such as the yeast PHO5.

Induction of apoptosis in lymphoid and myeloid leukemia

Defects in the core machinery of the apoptosis pathway contribute to chemoresistance and poor outcomes in patients with acute leukemia. To overcome these defects, novel molecules that target key proteins in the apoptosis pathway are being developed. This review highlights compounds that target the mitochondrial, death receptor, and convergence pathways of caspase activation that are being developed for the treatment of acute leukemia.

Targeting caspase 8 to reduce the formation of metastases in neuroblastoma

The clinical challenge in neuroblastoma is the presence of metastasis at diagnosis in the majority of patients. Caspase 8 is an integral protein in death receptor-associated apoptosis, and loss of caspase 8 via the epigenetic phenomenon of methylation in neuroblastoma has led to increased resistance to chemotherapy. Recent evidence suggests that caspase 8 loss may also contribute to a metastatic phenotype; thus, caspase 8 may prove to be an attractive target for therapy both in treating primary tumours as well as preventing and treating metastatic lesions. Numerous methods have been described to manipulate caspase 8 levels both in vitro and in vivo, and investigation into caspase 8 isoforms may also bring forth additional therapeutic targets.

Human, insect and nematode caspases kill Saccharomyces cerevisiae independently of YCA1 and Aif1p

This study characterised the impact of active metazoan apoptotic proteases (caspases) on Saccharomyces cerevisiae viability. Expression of active caspase-3 or caspase-8 in yeast ruptured plasma and nuclear membranes and dramatically impaired clonogenic survival, but did not damage DNA. Deletion of the proposed yeast apoptosis regulators YCA1 or Aif1p did not affect the ability of human, insect or nematode caspases to kill yeast. These data indicate that expression of active metazoan caspases causes irreversible damage to yeast membranes and organelles, in a manner independent of YCA1 and Aif1p.

Expression of survivin and correlation with PCNA in osteosarcoma

BACKGROUND AND OBJECTIVES

Survivin is a new anti-apoptosis gene with reported expression during fetal development and in cancer tissues. Proliferating cell nuclear antigen (PCNA) is essential for the replication of deoxyribonucleic acid (DNA). In this experiment, we examined the expression of survivin and PCNA in human osteosarcoma tissues and investigating whether survivin and PCNA expressions were correlated with histological grades, histological types, and patients' clinical characteristics.

METHODS

Sixty-eight osteosarcoma samples were divided into two groups based on the degree of tumor cell differentiation. Immunohistochemical staining was performed to analyze the expression of survinin and PCNA. Four histological types and patients' clinical characteristics were also recorded.

RESULTS

There were abundant levels of survivin and PCNA immunoreactivity in the nucleus and/or cytoplasm of the osteosarcoma cells. All cells essentially revealed the cytoplasmic localization and the nuclear signals of survivin in same cases, while PCNA from the majority of cases predominantly showed nuclear expression. Scoring on the percentage of positive cells indicated that survivin expression was significantly associated with the PCNA-labeling index (LI), which was correlated with the histological grades of osteosarcoma (chi2 = 17.86 and chi2 = 23.75, respectively).

CONCLUSIONS

The expression of survivin can be used as a useful indicator in grading the malignancy of osteosarcoma.

Human Bcl-2 cannot directly inhibit the Caenorhabditis elegans Apaf-1 homologue CED-4, but can interact with EGL-1

Although the anti-apoptotic activity of Bcl-2 has been extensively studied, its mode of action is still incompletely understood. In the nematode Caenorhabditis elegans, 131 of 1090 somatic cells undergo programmed cell death during development. Transgenic expression of human Bcl-2 reduced cell death during nematode development, and partially complemented mutation of ced-9, indicating that Bcl-2 can functionally interact with the nematode cell death machinery. Identification of the nematode target(s) of Bcl-2 inhibition would help clarify the mechanism by which Bcl-2 suppresses apoptosis in mammalian cells. Exploiting yeast-based systems and biochemical assays, we analysed the ability of Bcl-2 to interact with and regulate the activity of nematode apoptosis proteins. Unlike CED-9, Bcl-2 could not directly associate with the caspase-activating adaptor protein CED-4, nor could it inhibit CED-4-dependent yeast death. By contrast, Bcl-2 could bind the C. elegans pro-apoptotic BH3-only Bcl-2 family member EGL-1. These data prompt us to hypothesise that Bcl-2 might suppress nematode cell death by preventing EGL-1 from antagonising CED-9, rather than by inhibiting CED-4.

Are yeasts free-living unicellular eukaryotes?

Yeasts are defined as unicellular fungi, yet many recent observations suggest their whole lifestyle is anything but unicellular. This review surveys the evidence that yeasts are really social organisms with cell-to-cell communication.

The Caenorhabditis elegans CED-9 protein does not directly inhibit the caspase CED-3, in vitro nor in yeast

A genetically defined pathway orchestrates the removal of 131 of the 1090 somatic cells generated during the development of the hermaphrodite nematode Caenorhabditis elegans. Regulation of apoptosis is highly evolutionarily conserved and the nematode cell death pathway is a valuable model for studying mammalian apoptotic pathways, the dysregulation of which can contribute to numerous diseases. The nematode caspase CED-3 is ultimately responsible for the destruction of worm cells in response to apoptotic signals, but it must first be activated by CED-4. CED-9 inhibits programmed cell death and considerable data have demonstrated that CED-9 can directly bind and inhibit CED-4. However, it has been suggested that CED-9 may also directly inhibit CED-3. In this study, we used a yeast-based system and biochemical approaches to explore this second potential mechanism of action. While we confirmed the ability of CED-9 to inhibit CED-4, our data argue that CED-9 can not directly inhibit CED-3.

Yeast Programmed Cell Death: An Intricate Puzzle

Yeasts as eukaryotic microorganisms with simple, well known and tractable genetics, have long been powerful model systems for studying complex biological phenomena such as the cell cycle or vesicle fusion. Until recently, yeast has been assumed as a cellular 'clean room' to study the interactions and the mechanisms of action of mammalian apoptotic regulators. However, the finding of an endogenous programmed cell death (PCD) process in yeast with an apoptotic phenotype has turned yeast into an 'unclean' but even more powerful model for apoptosis research. Yeast cells appear to possess an endogenous apoptotic machinery including its own regulators and pathway(s). Such machinery may not exactly recapitulate that of mammalian systems but it represents a simple and valuable model which will assist in the future understanding of the complex connections between apoptotic and non-apoptotic mammalian PCD pathways. Following this line of thought and in order to validate and make the most of this promising cell death model, researchers must undoubtedly address the following issues: what are the crucial yeast PCD regulators? How do they play together? What are the cell death pathways shared by yeast and mammalian PCD? Solving these questions is currently the most pressing challenge for yeast cell death researchers.

Functional characterization of human proapoptotic molecules in yeastS. cerevisiae

The presence of a complete (BH1-3) proapoptotic molecule is necessary for the induction of the intrinsic apoptotic cascade in mammalian cells. It is unclear, however, what distinct roles the members of the large family of BH3-only proapoptotic molecules play in apoptosis. Although biochemical analysis of these molecules can characterize binding efficiencies of BH3 family members, the biologic consequences of these interactions are difficult to predict. We have, therefore, established three functional categories of BH3-only human proapoptotic proteins based on their toxicity after expression in budding yeast: directly killing (tBid), sensitizing in Bax/Bcl-2 expressing cells (Bad or Puma), and non-toxic (BNip3, BNip3L, and Noxa). The mechanism of killing by the proapoptotic molecules in yeast, however, is not due to activation of the recently described yeast metacaspase MCA1.

Inhibitor of apoptosis proteins: translating basic knowledge into clinical practice

The inhibitor of apoptosis proteins (IAPs) are a family of antiapoptotic proteins that bind and inhibit caspases 3, 7, and/or 9, but not caspase 8. Growing evidence also indicates that IAPs also modulate cell division, cell cycle progression, and signal transduction pathways. As our basic understanding of IAPs has increased, the knowledge is being translated into clinically useful applications in the diagnosis and treatment of malignancy. For example, IAPs such as survivin are being investigated as diagnostic markers for the presence of occult malignancy. In addition, IAP overexpression is a poor prognostic marker in a variety of solid tumors and hematologic malignancies. Finally, IAPs are attractive therapeutic targets, and efforts are under way to develop antisense and chemical IAP inhibitors that may be useful for the treatment of a variety of malignancies. For all of these potential clinical applications, however, the challenge remains to incorporate these findings into actual clinical practice.

Involvement of caspase-10 in advanced glycation end-product-induced apoptosis of bovine retinal pericytes in culture

Apoptosis appears to be the death mechanism of pericyte loss observed in diabetic retinopathy. We have previously shown that advanced glycation end-products (AGE-MGX) induce apoptosis of retinal pericytes in culture associated with diacylglycerol (DAG)/ceramide production. In the present study, we investigated possible caspase involvement in this process. Bovine retinal pericytes (BRP) were cultured with AGE-MGX and apoptosis examined after annexin V staining. Effects of peptidic inhibitors of caspases were determined on DAG/ceramide production and apoptosis. Pan-caspase inhibitor z-VAD-fmk (50 microM) was able to inhibit both DAG/ceramide production and apoptosis, whereas caspase-3-like inhibitor z-DEVD-fmk (50 microM) or caspase-9 inhibitor z-LEHD-fmk (50 microM) was only active on apoptosis. This differential effect strongly suggests involvement of initiator caspase(s) upstream and effector caspase(s) downstream DAG/ceramide production in AGE-mediated apoptosis. Pericyte treatment with caspase-8 inhibitor z-IETD-fmk (50 microM) did not protect cells against AGE-induced apoptosis and we failed to detect caspase-8 in pericytes by immunoblotting assay. Interestingly, one inhibitor of caspase-10 and related caspases z-AEVD-fmk (50 microM) inhibited both AGE-MGX-induced apoptosis and DAG/ceramide formation in pericytes. Cleavage of caspase-10 precursor into its active subunits was demonstrated by immunoblotting assay in pericytes incubated with AGE-MGX. These results strongly suggest that caspase-10, but not caspase-8, might be involved in the early phase of AGE-induced pericyte apoptosis, in contrast to caspase-9 and -3-like enzymes involved after DAG/ceramide production. This finding may provide new therapeutic perspectives for early treatment in diabetic retinopathy.

Differential gene expression in mononuclear phagocytes infected with pathogenic and non-pathogenic mycobacteria

The pathogenic mycobacteria are an insidious group of bacterial pathogens that cause the deaths of millions of people every year. One of the reasons these pathogens are so successful is that they are able to invade and replicate within host macrophages, one of the first lines of defence against intruding pathogens. In contrast, non-pathogenic mycobacteria, such as Mycobacterium smegmatis are killed rapidly by macrophages. In order to understand better the series of events that allow pathogenic mycobacteria to survive and replicate within macrophages, while the non-pathogenic mycobacteria are killed rapidly, we inoculated the human monocytic cell line U937 with pathogenic (M. tuberculosis and M. avium) and non-pathogenic (M. smegmatis) mycobacteria and monitored the expression of over 3500 genes at 4, 12 and 24 h post-inoculation using a commercially available gene array system. We observed multiple differences in the gene expression patterns of monocytes infected with pathogenic and non-pathogenic mycobacteria including genes involved in cytokine, lymphokine and chemokine production, adhesion, apoptosis, signal transduction, transcription, protein cleavage, actin polymerization and growth. We also observed differences in gene expression profiles in monocytes infected with M. tuberculosis or M. avium, indicating that there are differences in the host pathogen interactions of mononuclear phagocytes infected with different pathogenic mycobacterial species. These results increase the understanding of the mechanisms used by pathogenic mycobacteria to cause disease, the host response to these organisms, and provide new insights for antimycobacterial intervention strategies.

Mice overexpressing human caspase 3 appear phenotypically normal but exhibit increased apoptosis and larger lesion volumes in response to transient focal cerebral ischaemia

Caspase 3 activation has been implicated in cell death following a number of neurodegenerative insults. To determine whether caspase genes can affect the susceptibility of cells to neurodegeneration, a transgenic mouse line was created, expressing human caspase 3 under control of its own promoter. The human gene was regulated by the murine homeostatic machinery and human procaspase 3 was expressed in the same tissues as mouse caspase 3. These novel transgenic mice appeared phenotypically and developmentally normal and survived in excess of 2 years. Behavioural assessment using the 5-choice serial reaction time task found no differences from wild-type littermates. Caspase activity was found to be tightly regulated under physiological conditions, however, significantly larger lesions were obtained when transgenic mice were subjected to focal cerebral ischaemia/reperfusion injury compared to wild-type littermates. These data demonstrate that mice overexpressing human caspase 3 are essentially normal, however, they have increased susceptibility to degenerative insults.

Disruption of gamma-glutamylcysteine synthetase results in absolute glutathione auxotrophy and apoptosis in Candida albicans

Glutathione is the most abundant non-protein thiol and a major source of reducing equivalents in eukaryotes. We examined the role of glutathione in Candida albicans by the disruption of gamma-glutamylcysteine synthetase (GCS1), an essential enzyme in glutathione biosynthesis. The gcs1/gcs1 null mutants exhibited glutathione auxotrophy, which could be rescued by supplementing with reduced and oxidized glutathione and gamma-glutamylcysteine. When the mutants were depleted of glutathione, they showed typical markers of apoptosis. These results suggest that glutathione itself is an essential metabolite and C. albicans lacking GCS1 undergoes apoptosis.

Heterologous expression of maize (Zea mays L.) Mir1 cysteine proteinase in eukaryotic and prokaryotic expression systems

Several heterologous expression systems were tested for their ability to express a unique maize cysteine proteinase Mir1. A baculovirus-based expression system using Trichoplusia ni larvae as host resulted in the expression of Mir1 that was correctly processed and exhibited proteinase activity. Expression in Escherichia coli resulted in accumulation of Mir1, but it had limited solubility and enzymatic activity. Large quantities of Mir1 were produced when Pichia pastoris was used as the host, but the enzyme was insoluble and inactive.

Caspase activity is not sufficient to execute cell death

Molecular studies of the physiological cell death process have focused attention on the role of effector caspases as critical common elements of the lethal mechanism. Diverse death signals act afferently via distinct signaling pathways to activate these resident proenzyme molecules post-translationally. Whether this molecular convergence represents the mechanistic point of irreversible commitment to cell death has not been established. That a number of caspase substrates are proteins that serve important roles in cellular homeostasis has led to the view that the acquisition of this activity must be the determinative step in cell death. Observations that caspases serve in a regulatory role to catalyze the appearance of new activities involved in orderly cellular dissolution challenge this model of death as a simple process of proteolytic destruction. We found previously that caspase-dependent nuclear cyclin dependent kinase 2 (Cdk2) activity appears to be necessary for cell death. Employing direct cytofluorimetric analyses of intracellular caspase activity and colony forming assays, we now show that transient blockade of caspase-dependent Cdk2 activity confers long-lived sparing from death on cells otherwise triggered to die and fully replete with caspase activity. These data demonstrate that caspases, while necessary for apoptosis, are not sufficient to exert lethality. Caspase activation per se does not represent an irreversible point of commitment to physiological cell death.

HMGB1 inhibits cell death in yeast and mammalian cells and is abundantly expressed in human breast carcinoma

Apoptosis is a fundamental biological process used to eliminate unwanted cells in a multicellular organism. An increasing number of regulatory proteins have been identified that either promote or inhibit apoptosis. For tumors to arise, apoptosis must be blocked in the transformed cells, for example by mutational overexpression of anti-apoptotic proteins, which represent attractive target proteins for molecular therapy strategies. In a functional yeast survival screen designed to select new anti-apoptotic mammalian genes, we have identified the chromosomal high-mobility group box-1 protein (HMGB1) as an inhibitor of yeast cell death induced by the pro-apoptotic Bcl-2 family member Bak. The C-terminal 33 amino acids of HMGB1 are dispensable for this inhibitory function. HMGB1 is also able to protect mammalian cells against different death stimuli including ultraviolet radiation, CD95-, TRAIL-, Casp-8-, and Bax-induced apoptosis. We found high HMGB1 protein levels in human primary breast carcinoma. Hmgb1 RNA levels are changing during different stages of mouse mammary gland development and are particularly low during lactation and involution. These data suggest that HMGB1 may participate in the regulation of mammary gland apoptosis and that its high expression level promotes tumor growth because of its anti-apoptotic properties.

Bcl-2 family members inhibit oxidative stress-induced programmed cell death in Saccharomyces cerevisiae

Selected antiapoptotic genes were expressed in baker's yeast (Saccharomyces cerevisiae) to evaluate cytoprotective effects during oxidative stress. When exposed to treatments resulting in the generation of reactive oxygen species (ROS), including H(2)O(2), menadione, or heat shock, wild-type yeast died and exhibited apoptotic-like characteristics, consistent with previous studies. Yeast strains were generated expressing nematode ced-9, human bcl-2, or chicken bcl-xl genes. These transformants tolerated a range of oxidative stresses, did not display features associated with apoptosis, and remained viable under conditions that were lethal to wild-type yeast. Yeast strains expressing a mutant antiapoptotic gene (bcl-2 deltaalpha 5-6), known to be nonfunctional in mammalian cells, were unable to tolerate any of the ROS-generating insults. These data are the first report showing CED-9 has cytoprotective effects against oxidative stress, and add CED-9 to the list of Bcl-2 protein family members that modulate ROS-mediated programmed cell death. In addition, these data indicate that Bcl-2 family members protect wild-type yeast from physiological stresses. Taken together, these data support the concept of the broad evolutionary conservation and functional similarity of the apoptotic processes in eukaryotic organisms.

S29 ribosomal protein induces apoptosis in H520 cells and sensitizes them to chemotherapy

Non-small cell lung cancer (NSCLC) is the most prevalent type of lung cancer especially in India and displays resistance to anticancer treatment. In our earlier study we had isolated a cDNA clone from rat thymocytes induced to undergo apoptosis, which was found to encode S29 ribosomal protein [Biochem. Biophys. Res. Commun. 277 (2000) 476]. In the present study an attempt has been made to find out whether enhanced expression of S29 cDNA can kill NSCLC H520 cells. We found that S29 induced apoptosis and augmented the effect of anticancer drugs. Expressions of several molecular determinants of apoptosis were analyzed in order to understand the mechanism of apoptosis induced by S29. We observed downregulation of the expression of inhibitors of apoptosis proteins (IAPs) Bcl-2, Bcl-X(L), and survivin and upregulation of pro-apoptotic p53 and Bax as assessed by Western blotting. Mitochondrial release of cytochrome c and activation of initiator caspase-8 and -9 and effector caspase-3, followed by cleavage of nuclear substrate poly(ADP-ribose) polymerase, were also observed. Permeability transition as determined by changes in DeltaPsi(m) was not a requirement for cytochrome c release. There was a marginal increase in the release of apoptosis inducing factor (AIF) and reduction of NF-kappaB dependent transcriptional activity. There was non-involvement of calcium and the telomerase activity, a proliferation marker.

Human beta-secretase activity in yeast detected by a novel cellular growth selection system

Sequential processing of the transmembrane amyloid precursor protein (APP) by the beta-secretase BACE and by the gamma-secretase causes secretion of Abeta peptides. Extracellular aggregation of these peptides in the brain is a major hallmark of Alzheimer's disease. For therapeutic purposes and the development of specific inhibitors, it is important to characterize these secretases. We have established a cellular growth selection system for functional expression of human BACE in the yeast Saccharomyces cerevisiae. A fragment of APP bearing the beta-site, the transmembrane domain and the cytosolic tail was fused to the C-terminus of the yeast enzyme invertase, which is normally secreted to allow cell growth in the presence of sucrose as the sole carbon source. The resulting invertase-APP fusion protein was expressed as a type-I transmembrane protein in intracellular compartments of yeast cells lacking endogenous invertase. In these cells, co-expression of human BACE restored cell growth on selective plates upon cleavage of the invertase-APP fusion protein. The cellular growth selection system presented here can be generally applied to screen for secretases that specifically cleave membrane-bound substrates. Furthermore, this system provides the basis for a high-throughput screen for identifying secretase inhibitors that are active in eukaryotic cells.

Programmed cell death in trypanosomatids and other unicellular organisms

In multicellular organisms, cellular growth and development can be controlled by programmed cell death (PCD), which is defined by a sequence of regulated events. However, PCD is thought to have evolved not only to regulate growth and development in multicellular organisms but also to have a functional role in the biology of unicellular organisms. In protozoan parasites and in other unicellular organisms, features of PCD similar to those in multicellular organisms have been reported, suggesting some commonality in the PCD pathway between unicellular and multicellular organisms. However, more extensive studies are needed to fully characterise the PCD pathway and to define the factors that control PCD in the unicellular organisms. The understanding of the PCD pathway in unicellular organisms could delineate the evolutionary origin of this pathway. Further characterisation of the PCD pathway in the unicellular parasites could provide information regarding their pathogenesis, which could be exploited to target new drugs to limit their growth and treat the disease they cause.

Cancer therapeutics in yeast

The budding yeast Saccharomyces cerevisiae is a genetically tractable model system with which to establish the cellular target of a given agent and investigate mechanisms of drug action.

Bax expression protects yeast plasma membrane against ethanol-induced permeabilization

The mechanism by which the expression of pro-apoptotic protein Bax is able to kill yeast was investigated. Ethanol stress induces a permeabilization of the plasma membrane revealed by propidium iodide accumulation. Bax expression, although killing yeast cells, prevents this permeabilization. These effects are modulated by aeration, by manipulation of the unsaturation index of fatty acids and by addition of resveratrol, a known inhibitor of lipid oxidation. These data suggest that lipid oxidation is involved in Bax effects. Taken together, these data show for the first time a direct effect of Bax on plasma membrane permeability properties and suggest that yeast is a powerful tool for investigating the molecular mechanisms underlying this process.

Yeast and apoptosis

Even though yeast lack much of the molecular machinery that is responsible for apoptosis in metazoans, they can be a powerful tool in apoptosis research. The ectopic expression of several animal apoptosis proteins in yeast can help us to discover new genes -- and chemical compounds -- that modulate the cell-death pathways of higher eukaryotes.

A caspase-related protease regulates apoptosis in yeast

Yeast can undergo cell death accompanied by cellular markers of apoptosis. However, orthologs of classical mammalian apoptosis regulators appeared to be missing from the yeast genome, challenging a common mechanism of yeast and mammalian apoptosis. Here we investigate Yor197w, a yeast protein with structural homology to mammalian caspases, and demonstrate caspase-like processing of the protein. Hydrogen peroxide treatment induces apoptosis together with a caspase-like enzymatic activity in yeast. This response is completely abrogated after disruption and strongly stimulated after overexpression of Yor197w. Yor197w also mediates the death process within chronologically aged cultures, pointing to a physiological role in elimination of overaged cells. We conclude that Yor197w indeed functions as a bona fide caspase in yeast and propose the name Yeast Caspase-1 (YCA1, gene YCA1).

Signalling apoptosis: a radical approach

Reactive oxygen species (ROS) are frequently associated with cytotoxicity, often being described as damaging, harmful or toxic. It is generally assumed that, under pathological circumstances, ROS elicit wide-spread and random acts of oxidation. This passive attack of cellular components by ROS, in conditions where oxidative stress is the initiating stimulus for apoptosis, is assumed to simply trigger cell death as a result of cumulative oxidative damage. However, accumulating evidence now suggests that ROS may act as signalling molecules for the initiation and execution of the apoptotic death programme in many, if not all, current models of apoptotic cell death. Signalling by ROS would not appear to be random, as previously assumed, but targeted at specific metabolic and signal transduction cellular components. There is also evidence that the enzymatic generation of ROS may not simply be an unwanted by-product of the primary reaction catalysed, but that ROS may be used as signalling molecules to regulate cellular processes including apoptosis. This view of ROS as signalling molecules (as opposed to toxic metabolites) has been further bolstered by the findings that cellular antioxidants such as glutathione and thioredoxin not only serve to regulate ROS levels but also act as reversible redox modifiers of enzyme function. This review will attempt to delineate the involvement of ROS in apoptosis in light of these recent discoveries and provide evidence for a crucial role for ROS in the initiation and execution of the death process.

Phosphatidylinositol 3-kinase-dependent pathways oppose Fas-induced apoptosis and limit chloride secretion in human intestinal epithelial cells. Implications for inflammatory diarrheal states

The epithelial lining of the intestine serves as a barrier to lumenal bacteria and can be compromised by pathologic Fas-mediated epithelial apoptosis. Phosphatidylinositol (PI)3-kinase signaling has been described to limit apoptosis in other systems. We hypothesized that PI3-kinase-dependent pathways regulate Fas-mediated apoptosis and barrier function in intestiynal epithelial cells (IEC). IEC lines (HT-29 and T84) were exposed to agonist anti-Fas antibody in the presence or absence of chemical inhibitors of PI3-kinase (LY294002 and wortmannin). Apoptosis, barrier function, changes in short circuit current (DeltaI(sc)), and expression of adhesion molecules were assessed. Inhibition of PI3-kinase strongly sensitized IEC to Fas-mediated apoptosis. Expression of constitutively active Akt, a principal downstream effector of the PI3-kinase pathway, protected against Fas-mediated apoptosis to an extent that was comparable with expression of a genetic caspase inhibitor, p35. PI3-kinase inhibition sensitized to apoptosis by increasing and accelerating Fas-mediated caspase activation. Inhibition of PI3-kinase combined with cross-linking Fas was associated with increased permeability to molecules that were <400 Da but not those that were >3,000 Da. Inhibition of PI3-kinase resulted in chloride secretion that was augmented by cross-linking Fas. Confocal analyses revealed polymerization of actin and maintenance of epithelial cell adhesion molecule-mediated interactions in monolayers exposed to anti-Fas antibody in the context of PI3-kinase inhibition. PI3-kinase-dependent pathways, especially Akt, protect IEC against Fas-mediated apoptosis. Inhibition of PI3-kinase in the context of Fas signaling results in increased chloride secretion and barrier dysfunction. These findings suggest that agonists of PI3-kinase such as growth factors may have a dual effect on intestinal inflammation by protecting epithelial cells against immune-mediated apoptosis and limiting chloride secretory diarrhea.

Apoptosis in yeast: a new model for aging research

Apoptosis is a form of programmed cell death with a central role in development and homeostasis of metazoan organisms. Recent research indicates the presence of an apoptotic cell death program in unicellular eukaryotes. Yeast can be killed by expression of mammalian proapoptotic genes or in response to oxygen stress, which is an inducer of mammalian apoptosis. The dying yeast cells show morphological alterations typical for apoptosis. Yeast provides a simple model for cellular aging. The observation that old yeast cells produce oxygen radicals and die apoptotically may provide clues to a similar sequence of events in mammalian aging.