Physiological and pathological roles of Apaf1 and the apoptosome

Gestational Benzo[a]pyrene Exposure Destroys F1 Ovarian Germ Cells Through Mitochondrial Apoptosis Pathway and Diminishes Surviving Oocyte Quality

Polycyclic aromatic hydrocarbons, including benzo[a]pyrene (BaP), are products of incomplete combustion. In female mouse embryos primordial germ cells proliferate before and after arriving at the gonadal ridge around embryonic (E) 10 and begin entering meiosis at E13.5. Now oocytes, they arrest in the first meiotic prophase beginning at E17.5. We previously reported dose-dependent depletion of ovarian follicles in female mice exposed to 2 or 10 mg/kg-day BaP E6.5-15.5. We hypothesized that embryonic ovaries are more sensitive to gestational BaP exposure during the mitotic developmental window, and that this exposure results in persistent oxidative stress in ovaries and oocytes of exposed F1 female offspring. We orally dosed timed-pregnant female mice with 0 or 2 mg/kg-day BaP in oil from E6.5-11.5 (mitotic window) or E12.5-17.5 (meiotic window). Cultured E13.5 ovaries were utilized to investigate the mechanism of BaP-induced germ cell death. We observed statistically significant follicle depletion and increased ovarian lipid peroxidation in F1 pubertal ovaries following BaP exposure during either prenatal window. Culture of E13.5 ovaries with BaP induced germ cell DNA damage and release of cytochrome c from the mitochondria in oocytes, confirming that BaP exposure induced apoptosis via the mitochondrial pathway. Mitochondrial membrane potential, oocyte lipid droplet (LD) volume, and mitochondrial-LD colocalization were decreased and mitochondrial superoxide levels were increased in the MII oocytes of F1 females exposed gestationally to BaP. Results demonstrate similar sensitivity to germ cell depletion and persistent oxidative stress in F1 ovaries and oocytes following gestational BaP exposure during mitotic or meiotic windows.

Apoptosome Formation through Disruption of the K192-D616 Salt Bridge in the Apaf-1 Closed Form

The molecular mechanism of apoptosome activation through conformational changes of Apaf-1 auto-inhibited form remains largely enigmatic. The crystal structure of Apaf-1 suggests that some ionic bonds, including the bond between K192 and D616, are critical for the preservation of the inactive "closed" form of Apaf-1. Here, a split luciferase complementation assay was used to monitor the effect of disrupting this ionic bond on apoptosome activation and caspase-3 activity in cells. The K192E mutation, predicted to disrupt the ionic interaction with D616, increased apoptosome formation and caspase activity, suggesting that this mutation favors the "open"/active form of Apaf-1. However, mutation of D616 to alanine or lysine had different effects. While both mutants favored apoptosome formation such as K192E, D616K cannot activate caspases and D616A activates caspases poorly, and not as well as wild-type Apaf-1. Thus, our data show that the ionic bond between K192 and D616 is critical for maintaining the closed form of Apaf-1 and that disrupting the interaction enhances apoptosome formation. However, our data also reveal that after apoptosome formation, D616 and K192 play a previously unsuspected role in caspase activation. The molecular explanation for this observation is yet to be elucidated.

Pharmacological inhibition of mitochondrial fission attenuates oxidative stress-induced damage of retinal pigmented epithelial cells

Mitochondria maintain their function by the process of mitochondrial dynamics, which involves repeated fusion and fission. It is thought that the failure of mitochondrial dynamics, especially excessive fission, is related to the progression of several diseases. A previous study demonstrated that mitochondrial fragmentation occurs in the retinal pigmented epithelial (RPE) cells of patients with non-exudative age-related macular degeneration (AMD). We predicted that the suppression of mitochondrial fragmentation offers a novel therapeutic strategy for non-exudative AMD. We investigated whether the inhibition of mitochondrial fission was effective against the oxidative stress-induced damage of ARPE-19 cells. The treatment of ARPE-19 cells with H₂O₂ caused mitochondrial fragmentation, but treatment with mitochondrial division inhibitor 1 (Mdivi-1) suppressed fragmentation. Additionally, Mdivi-1 protected ARPE-19 cells against H₂O₂-induced damage, and suppressed the release of cytochrome c from the mitochondria. Mitochondrial function was evaluated by staining with JC-1 and measuring the production of reactive oxygen species (ROS), which revealed that mitochondrial function improved in the Mdivi-1-treated group. These findings indicated that the inhibition of mitochondrial fission would be a novel therapeutic target for non-exudative AMD.

Long Non-coding RNA TALNEC2 Aggravates Cerebral Ischemia/Reperfusion Injury via Acting as a Competing Endogenous RNAs for miR-650 to Target Apoptotic Peptidase Activating Factor 1

Increasing evidence has indicated that long non-coding RNAs (lncRNAs) play a vital role for adjusting RNA transcripts as competing endogenous RNAs (ceRNAs) for microRNAs (miRNAs). The present study was intended to explore the probable regulation of lncRNA TALNEC2 in ischemic stroke. In this study, we measured the up-regulation of TALNEC2 and down-regulation of miR-650 in mice brains after cerebral ischemia/reperfusion (I/R) operation and in cultured neuroblastoma cells of neuro-2A (N2a) treated with oxygen glucose deprivation/reoxygenation (OGD/R). Then we verified the common predicted binding sites of miR-650 in TALNEC2 and 3'-UTR of apoptotic peptidase activating factor 1 (APAF1), a critical regulator in ischemic neuronal death, with bioinformatics. Overexpression of miR-650 reduced N2a cell apoptosis induced by OGD/R. MiR-650 was confirmed to be a directly target of APAF1 by luciferase reporter assay. It was found that TALNEC2 played a critical role as a ceRNA for miR-650 and bound directly to miR-650 to mediate the APAF1. In result, overexpression of TALNEC2 antagonized the inhibition impact of miR-650 on APAF1 expression and N2a cell apoptosis induced by OGD/R, while TALNEC2 knockdown aggravated the impact. Furthermore, TALNEC2 knockdown reversed brain injury and neurological deficits induced by I/R in vivo. In conclusion, we verified a TALNEC2/miR-650/APAF1 signaling pathway as a key mechanism monitoring cerebral I/R injury.

The effects of a short-term exposure to propiconazole in zebrafish (Danio rerio) embryos

Propiconazole (PCZ) is a widely used fungicide around the world and was frequently detected in surface waters, which would pose risk to aquatic organisms. Previous studies indicated that PCZ has high toxicity to different kinds of fish. However, most of the studies focus on the toxicity and mechanisms of PCZ to adult fish, the potential toxicity mechanism of PCZ to fish embryos is still poorly understood. The present study investigated the effects of PCZ on content of reactive oxygen species (ROS) and malondialdehyde (MDA); activities of superoxide dismutase (SOD), catalase (CAT), and Na⁺-K⁺-ATPase; and expression level of genes related to oxidative stress, cell apoptosis, and innate immune system in zebrafish embryos after 96-h exposure. The results showed that 5.0 mg/L PCZ induced oxidative damage in zebrafish embryos, as indicated by increased ROS and MDA content and alteration of antioxidative enzyme activity. The activity of Na⁺-K⁺-ATPase in zebrafish embryos was significantly inhibited after exposure to 0.5 mg/L PCZ. The expression levels of bax, p53, casp-3, casp-9, and apaf-1 were significantly increased, indicating that cell apoptosis was caused in embryos by 5.0 mg/L PCZ. The expression level of interleukin-1b (IL-1b) and IL-8 increased after exposure to 0.5 mg/L PCZ, but that of IL-1b, IL-8, and cxcl-c1c (chemokine (C-X-C motif) ligand 18b) decreased in 5.0-mg/L PCZ treatment group, indicating an immunotoxicity effect. Our results suggest that oxidative damage, cell apoptosis, and immunotoxicity would be induced in zebrafish embryos after short-term exposure to PCZ.

In silico approach to the analysis of SNPs in the human APAF1 gene

The apoptotic protease activating factor 1 (APAF1) gene encodes a cytoplasmic protein that initiates apoptosis and is a crucial factor in the mitochondria-dependent death pathway. APAF1 is implicated in many pathways such as apoptosis, neurodegenerative diseases, and cancer. The purpose of this study was to predict deleterious/damaging SNPs in the APAF1 gene viain silicoanalysis. To this end, APAF1 missense SNPs were obtained from the NCBI dbSNP database. In silico analysis of the missense SNPs was carried out by using publicly available online software tools. The stabilization and three-dimensional modeling of mutant proteins were also determined by using the I-Mutant 2.0 and Project HOPE webservers, respectively. In total, 772 missense SNPs were found in the APAF1 gene from the NCBI dbSNP database, 18 SNPs of which were demonstrated to be deleterious or damaging. Of those, 13 SNPs had a decreasing effect on protein stability, while the other 5 SNPs had an increasing effect. Based on the modeling results, some dissimilarities of mutant type amino acids from wild-type amino acids such as size, charge, and hydrophobicity were revealed. The SNPs predicted to be deleterious in this study might be used in the selection of target SNPs for genotyping in disease association studies. Therefore, we could suggest that the present study could pave the way for future experimental studies.

CaDrA: A Computational Framework for Performing Candidate Driver Analyses Using Genomic Features

The identification of genetic alteration combinations as drivers of a given phenotypic outcome, such as drug sensitivity, gene or protein expression, and pathway activity, is a challenging task that is essential to gaining new biological insights and to discovering therapeutic targets. Existing methods designed to predict complementary drivers of such outcomes lack analytical flexibility, including the support for joint analyses of multiple genomic alteration types, such as somatic mutations and copy number alterations, multiple scoring functions, and rigorous significance and reproducibility testing procedures. To address these limitations, we developed Candidate Driver Analysis or CaDrA, an integrative framework that implements a step-wise heuristic search approach to identify functionally relevant subsets of genomic features that, together, are maximally associated with a specific outcome of interest. We show CaDrA's overall high sensitivity and specificity for typically sized multi-omic datasets using simulated data, and demonstrate CaDrA's ability to identify known mutations linked with sensitivity of cancer cells to drug treatment using data from the Cancer Cell Line Encyclopedia (CCLE). We further apply CaDrA to identify novel regulators of oncogenic activity mediated by Hippo signaling pathway effectors YAP and TAZ in primary breast cancer tumors using data from The Cancer Genome Atlas (TCGA), which we functionally validate in vitro. Finally, we use pan-cancer TCGA protein expression data to show the high reproducibility of CaDrA's search procedure. Collectively, this work demonstrates the utility of our framework for supporting the fast querying of large, publicly available multi-omics datasets, including but not limited to TCGA and CCLE, for potential drivers of a given target profile of interest.

The discovery of a novel inhibitor of apoptotic protease activating factor-1 (Apaf-1) for ischemic heart: synthesis, activity and target identification

Apaf-1 is a central component in the apoptosis regulatory network for the treatment of apoptosis related diseases. Excessive Apaf-1 activity induced by myocardial ischemia causes cell injury. No drug targeted to Apaf-1 for treating myocardial ischemia has been reported to the best of our knowledge. In the present work, we synthesized a novel compound, ZYZ-488, which exhibited significant cardioprotective property in significantly increasing the viability of hypoxia-induced H9c2 cardiomyocytes and reducing CK and LDH leakage. Further study suggested the protective activity of ZYZ-488 dependent on its anti-apoptosis effect. This anti-apoptotic effect is most probably related to its disturbing the interaction between Apaf-1 and procaspase-9 as the target fishing and molecular docking indicated. The suppression on the activation of procaspase-9 and procaspase-3 with ZYZ-488 strongly suggested that compound ZYZ-488 could be a novel inhibitor of Apaf-1. In conclusion, ZYZ-488 as a novel small molecule competitive inhibitor of Apaf-1, with the great potential for treating cardiac ischemia.

Decoding the oxidative stress hypothesis in diabetic embryopathy through proapoptotic kinase signaling

Maternal diabetes-induced birth defects occur in 6-10% of babies born to mothers with pregestational diabetes, representing a significant maternal-fetal health problem. Currently, these congenital malformations represent a significant maternal-fetal medicine issue, but are likely to create an even greater public health threat as 3 million women of reproductive age (19-44 years) have diabetes in the United States alone, and this number is expected to double by 2030. Neural tube defects (NTDs) and congenital heart defects are the most common types of birth defects associated with maternal diabetes. Animal studies have revealed that embryos under hyperglycemic conditions exhibit high levels of oxidative stress resulting from enhanced production of reactive oxygen species and impaired antioxidant capability. Oxidative stress activates a set of proapoptotic kinase signaling intermediates leading to abnormal cell death in the embryonic neural tube, which causes NTD formation. Work in animal models also has revealed that maternal diabetes triggers a series of signaling intermediates: protein kinase C (PKC) isoforms, PKCα, βII and δ; apoptosis signal-regulating kinase 1; c-Jun-N-terminal kinase (JNK)1/2; caspase; and apoptosis. Specifically, maternal diabetes in rodent models activates the proapoptotic unfolded protein response and endoplasmic reticulum (ER) stress. A reciprocal causation between JNK1/2 activation and ER stress exists in diabetic embryopathy. Molecular studies further demonstrate that deletion of the genes for Prkc, Ask1, Jnk1, or Jnk2 abolishes maternal diabetes-induced neural progenitor apoptosis and ameliorates NTD formation. Similar preventive effects are also observed when apoptosis signal-regulating kinase 1, JNK1/2, or ER stress is inhibited. Cell membrane stabilizers and antioxidant supplements are also effective in prevention of diabetes-induced birth defects. Mechanistic studies have revealed important insights into our understanding the cause of diabetic embryopathy and have provided a basis for future interventions against birth defects or other pregnancy complications associated with maternal diabetes. The knowledge of a molecular pathway map identified in animal studies has created unique opportunities to identify molecular targets for therapeutic intervention.

New concepts in diabetic embryopathy

Diabetes mellitus is responsible for nearly 10% of fetal anomalies in diabetic pregnancies. Although aggressive perinatal care and glycemic control are available in developed countries, the birth defect rate in diabetic pregnancies remains higher than that in the general population. Major cellular activities (ie, proliferation and apoptosis) and intracellular metabolic conditions (ie, nitrosative, oxidative, and endoplasmic reticulum stress) have been shown to be associated with diabetic embryopathy using animal models. Translating advances made in animal studies into clinical applications in humans requires collaborative efforts across the basic research, preclinical, and clinical communities.

Structure of an apoptosome-procaspase-9 CARD complex

Apaf-1 coassembles with cytochrome c to form the apoptosome, which then binds and activates procaspase-9 (pc-9). We removed pc-9 catalytic domains from the holoapoptosome by site-directed thrombinolysis. A structure of the resulting apoptosome-pc-9 CARD complex was then determined at approximately 9.5 A resolution. In our model, the central hub is constructed like other AAA+ protein rings but also contains novel features. At higher radius, the regulatory region of each Apaf-1 is comprised of tandem seven and eight blade beta-propellers with cytochrome c docked between them. Remarkably, Apaf-1 CARDs are disordered in the ground state. During activation, each Apaf-1 CARD interacts with a pc-9 CARD and these heterodimers form a flexibly tethered "disk" that sits above the central hub. When taken together, the data reveal conformational changes during Apaf-1 assembly that allow pc-9 activation. The model also provides a plausible explanation for the effects of NOD mutations that have been mapped onto the central hub.

Suppression of the intrinsic apoptosis pathway by synaptic activity

Synaptic activity promotes resistance to diverse apoptotic insults, the mechanism behind which is incompletely understood. We show here that a coordinated downregulation of core components of the intrinsic apoptosis pathway by neuronal activity forms a key part of the underlying mechanism. Activity-dependent protection against apoptotic insults is associated with inhibition of cytochrome c release in most but not all neurons, indicative of anti-apoptotic signaling both upstream and downstream of this step. We find that enhanced firing activity suppresses expression of the proapoptotic BH3-only member gene Puma in a NMDA receptor-dependent, p53-independent manner. Puma expression is sufficient to induce cytochrome c loss and neuronal apoptosis. Puma deficiency protects neurons against apoptosis and also occludes the protective effect of synaptic activity, while blockade of physiological NMDA receptor activity in the developing mouse brain induces neuronal apoptosis that is preceded by upregulation of Puma. However, enhanced activity can also confer resistance to Puma-induced apoptosis, acting downstream of cytochrome c release. This mechanism is mediated by transcriptional suppression of apoptosome components Apaf-1 and procaspase-9, and limiting caspase-9 activity, since overexpression of procaspase-9 accelerates the rate of apoptosis in active neurons back to control levels. Synaptic activity does not exert further significant anti-apoptotic effects downstream of caspase-9 activation, since an inducible form of caspase-9 overrides the protective effect of synaptic activity, despite activity-induced transcriptional suppression of caspase-3. Thus, suppression of apoptotic gene expression may synergize with other activity-dependent events such as enhancement of antioxidant defenses to promote neuronal survival.

The role of caspase-2 in stress-induced apoptosis

Caspase-2 is the most evolutionarily conserved of all the caspases, yet it has a poorly defined role in apoptotic pathways. This is mainly due to a dearth of techniques to determine the activation status of caspase-2 and the lack of an abnormal phenotype in caspase-2 deficient mice. Nevertheless, emerging evidence suggests that caspase-2 may have important functions in a number of stress-induced cell death pathways, in cell cycle maintenance and regulation of tumour progression. This review discusses recent advances that have been made to help elucidate the true role of this elusive caspase and the potential contribution of caspase-2 to the pathology of human diseases including cancer.

A structure of the human apoptosome at 12.8 A resolution provides insights into this cell death platform

Apaf-1 and cytochrome c coassemble in the presence of dATP to form the apoptosome. We have determined a structure of the apoptosome at 12.8 A resolution by using electron cryomicroscopy and single-particle methods. We then docked appropriate crystal structures into the map to create an accurate domain model. Thus, we found that seven caspase recruitment domains (CARDs) form a central ring within the apoptosome. At a larger radius, seven copies of the nucleotide binding and oligomerization domain (NOD) associate laterally to form the hub, which encircles the CARD ring. Finally, an arm-like helical domain (HD2) links each NOD to a pair of beta propellers, which bind a single cytochrome c. This model provides insights into the roles of dATP and cytochrome c in assembly. Our structure also reveals how a CARD ring and the central hub combine to create a platform for procaspase-9 activation.

Colchicine, a microtubule depolymerizing agent, inhibits myocardial apoptosis in rats

Heart failure is the most common cardiovascular disease with high mortality and morbidity. Both enhanced microtubule polymerization and cardiomyocyte apoptosis are involved in the pathogenesis of heart failure. However, the link between the two mechanisms remains to be elucidated. In this study, we thus address this important issue in cultured cardiomyocytes from Wistar rats in vitro and in angiotensin II (ATII)-infused rats in vivo. Confocal microscopy examination showed that in cultured rat cardiomyocytes, micrographic density of microtubules was increased by paclitaxel, a microtubule-polymerizing agent, and decreased by colchicine, a microtubule-depolymerizing agent, but not affected by ATII, isoproterenol, or tumor necrosis factor-alpha alone. Immunoblotting analysis showed that Bax/Bcl-2 ratio, which is associated with the activation of caspase-3, was significantly increased in ATII-stimulated cultured cardiomyocytes in vitro and in ATII-infused rats in vivo, both of which were inhibited by co-treatment with colchicine. Caspase-3 and TUNEL assay to detect apoptosis in vitro demonstrated that paclitaxel or ATII alone significantly enhanced and their combination further accelerated cardiomyocyte apoptosis, which was again significantly inhibited by colchicine. Caspase-3 and TUNEL assay in vivo also demonstrated that ATII infusion significantly increased myocardial apoptosis and that co-treatment with colchicine significantly suppressed the apoptosis. In conclusion, these results indicate that a microtubule-depolymerizing agent could be a potential therapeutic strategy for treatment of heart failure.

Incudomalleal joint formation: the roles of apoptosis, migration and downregulation

Background

The middle ear of mammals is composed of three endochondrial ossicles, the stapes, incus and malleus. Joints link the malleus to the incus and the incus to the stapes. In the mouse the first arch derived malleus and incus are formed from a single Sox9 and Type II collagen expressing condensation that later subdivides to give rise to two separate ossicles. In contrast the stapes forms from a separate condensation derived from the second branchial arch. Fusion of the malleus and incus is observed in a number of human syndromes and results in conductive hearing loss. Understanding how this joint forms during normal development is thus an important step in furthering our understanding of such defects.

Results

We show that the developing incudomalleal joint is characterised by a lack of proliferation and discrete areas of apoptosis. Apoptosis has been suggested to aid in the removal of pre-cartilaginous cells from the joint region, allowing for the physical separation of the cartilaginous elements, however, we show that joint initiation is unaffected by blocking apoptosis. There is also no evidence of cell migration out of the presumptive joint region, as observed by labelling of joint and ossicle cells in culture. Using Type II collagen lacZ reporter mice, however, it is evident that cells in the presumptive joint region remain in place and downregulate cartilage markers.

Conclusion

The malleus and incus first appear as a single united condensation expressing early cartilage markers. The incudomalleal joint region forms by cells in the presumptive joint region switching off cartilage markers and turning on joint markers. Failure in this process may result in fusion of this joint, as observed in human syndromes such as Branchio-Oto-Renal Syndrome or Treacher Collins Syndrome.

GAPDH and autophagy preserve survival after apoptotic cytochrome c release in the absence of caspase activation

In cells undergoing apoptosis, mitochondrial outer-membrane permeabilization (MOMP) is followed by caspase activation promoted by released cytochrome c. Although caspases mediate the apoptotic phenotype, caspase inhibition is generally not sufficient for survival following MOMP; instead cells undergo a "caspase-independent cell death" (CICD). Thus, MOMP may represent a point of commitment to cell death. Here, we identify glyceraldehyde-3-phosphate dehydrogenase (GAPDH) as a critical regulator of CICD. GAPDH-expressing cells preserved their clonogenic potential following MOMP, provided that caspase activation was blocked. GAPDH-mediated protection of cells from CICD involved an elevation in glycolysis and a nuclear function that correlated with and was replaced by an increase in Atg12 expression. Consistent with this, protection from CICD reflected an increase in and a dependence upon autophagy, associated with a transient decrease in mitochondrial mass. Therefore, GAPDH mediates an elevation in glycolysis and enhanced autophagy that cooperate to protect cells from CICD.

Lack of apoptotic protease activating factor-1 expression and resistance to hypoxia-induced apoptosis in cervical cancer

PURPOSE

Clinical observations suggest that intratumoral hypoxia increases the aggressiveness of tumors through clonal selection of cancer cells that have lost their apoptotic potential. The aim of this study, therefore, was to investigate the expression of the proapoptotic protein apoptotic protease activating factor-1 (Apaf-1) in cervical cancers and to analyze its relation to intratumoral hypoxia and apoptosis. Furthermore, the effect of hypoxia and apoptosis on survival was examined.

EXPERIMENTAL DESIGN

In 56 patients, intratumoral oxygenation measurements and subsequent needle biopsies were done. The obtained tissue was analyzed by terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assays and by immunohistochemistry with an Apaf-1 antibody.

RESULTS

Apaf-1 was expressed in 86% of cancers. The median apoptosis rate was 1.0%. There was no correlation between Apaf-1 expression and intratumoral hypoxia. However, Apaf-1 expression was negative in 37.5% of hypoxic cervical cancers (pO(2) <or= 10 mmHg) with low apoptosis rates (<or=1.0%) compared with only 5.0% in nonhypoxic cancers and hypoxic cancers with high apoptosis (P = 0.005; Fisher's exact test). With a median follow-up period of 44 months, there was a nonsignificant trend toward worse prognosis in the hypoxic low-apoptotic group (P = 0.08).

CONCLUSIONS

Although Apaf-1 is expressed in the vast majority of cervical cancers, a significant proportion of tumors with low apoptosis rates despite intratumoral hypoxia showed a lack of Apaf-1 expression. This finding suggests that loss of Apaf-1 expression is a mechanism by which hypoxic cervical cancers acquire resistance to apoptosis. Thus, low Apaf-1 expression in hypoxic tumors may be an unfavorable prognostic factor.

Caspase-11 regulates cell migration by promoting Aip1-Cofilin-mediated actin depolymerization

Coordinated regulation of cell migration, cytokine maturation and apoptosis is critical in inflammatory responses. Caspases, a family of cysteine proteases, are known to regulate cytokine maturation and apoptosis. Here, we show that caspase-11, a mammalian pro-inflammatory caspase, regulates cell migration during inflammation. Caspase-11-deficient lymphocytes exhibit a cell-autonomous migration defect in vitro and in vivo. We demonstrate that caspase-11 interacts physically and functionally with actin interacting protein 1 (Aip1), an activator of cofilin-mediated actin depolymerization. The caspase-recruitment domain (CARD) of caspase-11 interacts with the carboxy-terminal WD40 propeller domain of Aip1 to promote cofilin-mediated actin depolymerization. Cells with Aip1 or caspase-11 deficiency exhibit defects in actin dynamics. Using in vitro actin depolymerization assays, we found that caspase-11 and Aip1 work cooperatively to promote cofilin-mediated actin depolymerization. These data demonstrate a novel cell autonomous caspase-mediated mechanism that regulates actin dynamics and mammalian cell migration distinct from the receptor mediated Rho-Rac-Cdc42 pathway.

Matrine upregulates the cell cycle protein E2F-1 and triggers apoptosis via the mitochondrial pathway in K562 cells

Matrine is a major component of Sophora Flavescens and has been reported to stimulate differentiation of erythroleukemia cells. Here we show that matrine inhibits cell proliferation or induces apoptosis in a cell type-specific manner. The latter effect was investigated in more detail in the p53 deficient erythroleukemia cell line, K562. Matrine exposure induced apoptosis in a time- and dose-dependent manner in these cells. Interestingly, co-treatment with etoposide potentiated apoptosis. Further analysis of matrine-induced apoptotic changes revealed that E2F-1 and Apaf-1 were upregulated, whereas Rb was downregulated after 24 h of exposure. This was followed by Bax translocation, cytochrome c release, and caspase-9 and -3 activation. These results demonstrate that matrine triggers apoptosis of K562 cells primarily through the mitochondrial pathway and that matrine is a potential anti-tumor drug.

Mechanisms of expression of apoptotic protease activating factor-1 (Apaf-1) in nuclear, mitochondrial and cytosolic fractions of the cerebral cortex of newborn piglets

Apoptotic protease activating factor-1 (Apaf-1) is a critical regulator of apoptosis and a crucial part of the apoptosome that is assembled in response to several cellular stresses like hypoxia. We have previously shown that hypoxia results in increased influx of nuclear Ca(2+) and increased expression of nuclear apoptotic proteins. The present study investigates that Apaf-1 is expressed during hypoxia in the cerebral cortex of newborn piglets and that administration of clonidine prevents the hypoxia induced increase expression of Apaf-1. Studies were conducted in 19 newborn piglets, 6 normoxic (Nx), 7 hypoxic (Hx FiO(2) of 0.05-0.07 for 1h) and 6 clonidine-treated hypoxic (Hx-Clo) piglets. Tissue hypoxia was confirmed biochemically by determining the levels of high energy phosphates ATP and phosphocreatine (PCr). Neuronal nuclei, mitochondrial membranes and cytosolic fractions were isolated and separated by 12% SDS-PAGE and probed with specific antibodies to Apaf-1. The expression of Apaf-1 in neuronal nuclei was 48.86+/-5.27 in Nx, 108.43+/-6.37 in Hx and 78.53+/-7.00 in Hx-Clo. The Apaf-1 expression of in mitochondrial fraction was 72.73+/-11.76 in Nx, 132.27+/-16.15 in Hx and 85.17+/-5.64 in Hx-Clo. Similarly, the expression of Apaf-1 in cytosolic fraction was 86.79+/-6.97 in Nx, 193.95+/-15.41 in Hx and 111.07+/-7.91 in Hx-Clo. In summary, the results show that hypoxia results in increased expression of Apaf-1 proteins in neuronal nuclear, mitochondrial and cytosolic fractions. Administration of a high affinity Ca(2+)-ATPase, prevented the hypoxia induced increased expression of Apaf-1 protein, suggesting that the hypoxia-induced increased expression of Apaf-1 proteins is nuclear Ca(2+)-influx mediated. We conclude that cerebral hypoxia-induced increase in Apaf-1 protein will lead to increased activation of procaspase-9 to caspase-9 in the cytosolic compartment leading to a cascade of hypoxic neuronal death.

Primary enamel knot cell death in Apaf-1 and caspase-9 deficient mice

During molar development, apoptosis occurs in a well-characterised pattern suggesting several roles for cell death in odontogenesis. However, molecular mechanisms of dental apoptosis are only poorly understood. In this study, Apaf-1 and caspase-9 knockouts were used to uncover the engagement of these members of the apoptotic machinery during early tooth development, concentrating primarily on their function in the apoptotic elimination of primary enamel knot cells. Molar tooth germ morphology, proliferation and apoptosis were investigated on frontal histological sections of murine heads at embryonic days (ED) 15.5, the stage when the primary enamel knot is eliminated apoptotically. In molar tooth germs of both knockouts, no apoptosis was observed according to morphological (haematoxylin-eosin) as well as biochemical criteria (TUNEL). Morphology of the mutant tooth germs, however, was not changed. Additionally, knockout mice showed no changes in proliferation compared to wild type mice. According to our findings on knockout embryos, Apaf-1 and caspase-9 are involved in apoptosis during tooth development; however, they seem dispensable and not necessary for proper tooth shaping. Compensatory or other mechanisms of cell death may act to eliminate the primary enamel knot cells in the absence of Apaf-1 and caspase-9.

Divergence from a dedicated cellular suicide mechanism: exploring the evolution of cell death

The developmental cell death in the nematode C. elegans is controlled by a simple and dedicated genetic program. This genetic program is evolutionarily conserved in higher organisms, including mammals. However, although mammalian homologs of C. elegans cell death gene products continue to regulate apoptosis, they are no longer dedicated regulators of cell death. On the other hand, multiple cellular noncell death-related mechanisms have been recruited to regulate cell death under different conditions. Such evidence suggests that evolution has led to an extensive integration of mammalian apoptosis machinery with multiple cellular physiological processes.

Do Alix and ALG-2 really control endosomes for better or for worse?

Alix/AIP1 (ALG-2-interacting protein X/apoptosis-linked-gene-2-interacting protein 1) is an adaptor protein that was first described for its capacity to bind to the calcium-binding protein ALG-2 (apoptosis-linked gene 2), the expression of which seemed necessary for cell death. Over-expression of truncated forms of Alix blocks caspase-dependent and -independent mechanisms of cell death. Numerous observations in yeast and in mammalian cells suggest that Alix controls the making of and trafficking through endosomes called MVBs (multivesicular bodies), which are crucial intermediates within the endolysosomal system. In particular, deletion of Bro1, one of the yeast homologues of Alix, leads to an impairment in the function of MVBs, leading to mis-sorting of proteins normally destined to the vacuole. Mammalian Alix may have a similar function and has been shown to bind to lyso(bis)phosphatidic acid, ESCRT (endosomal sorting complex required for transport) proteins, endophilins and CIN85 (Cbl-interacting protein of 85 kDa), which are all main regulators of the endosomal system. EIAV (equine infectious anaemia virus) and HIV late domains use Alix to recruit the ESCRT machinery in order to bud from the cell surface, underscoring the crucial role of the protein in orchestrating membrane deformation. In this review I develop the hypothesis that the normal function of Alix in the endolysosomal system may be deviated by ALG-2 towards a destructive role during active cell death.

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.

Reduction of Caspase-8 and -9 Cleavage Is Associated With Increased c-FLIP and Increased Binding of Apaf-1 and Hsp70 After Neonatal Hypoxic/Ischemic Injury in Mice Overexpressing Hsp70

Background and Purpose— Caspase-8 and caspase-9 are essential proteases of the extrinsic and intrinsic apoptotic pathways, respectively. We investigated whether neuroprotection associated with overexpression of heat-shock protein 70 (Hsp70), a natural cellular antiapoptotic protein, is mediated by caspase-8 and caspase-9 signaling in the neonatal mouse brain after hypoxia/ischemia (H/I) injury.

Methods— Postnatal day 7 transgenic mice overexpressing rat Hsp70 (Hsp70 Tg) and their wild-type (Wt) littermates underwent unilateral common carotid artery ligation followed by 30 minutes of exposure to 8% O 2 . The expression of apoptotic proteins was quantified by Western blot analysis, and the specific interaction between Hsp70 and apoptotic protease activating factor 1 (Apaf-1) was determined by coimmunoprecipitation.

Results— Hsp70 overexpression reduced cytosolic translocation of cytochrome c without affecting the levels of Apaf-1 and pro–caspase-9 24 hours after H/I. The expression of these apoptotic proteins in the naïve neonatal brains was also not affected by Hsp70 overexpression. Reduced caspase-9 cleavage occurred in Hsp70 Tg mice compared with Wt littermates 24 hours after H/I and correlated with increased binding of Hsp70 and Apaf-1. Increased cellular Fas-associated death domain–like interleukin-1β–converting enzyme inhibitory protein (FLIP) expression and decreased caspase-8 cleavage were also observed in Hsp70 Tg compared with Wt mice 24 hours after H/I.

Conclusions— Our results suggest that the extrinsic and intrinsic apoptotic pathways mediate the neuroprotective effects of Hsp70 overexpression in neonatal H/I, specifically by upregulating FLIP and sequestering Apaf-1, leading to reduced cleavage of caspase-8 and caspase-9.

The predictive value of apoptosis protease-activating factor 1 in rectal tumors treated with preoperative, high-dose-rate brachytherapy

BACKGROUND

The objective of this study was to assess the value of apoptosis protease-activating factor 1 (APAF-1) as a predictive marker of response in rectal tumors treated with preoperative, high-dose-rate endorectal brachytherapy.

METHODS

Immunohistochemistry for APAF-1 was performed on 94 rectal tumor biopsy specimens from patients who were treated on a preoperative, high-dose-rate brachytherapy protocol. Tumors were considered positive when > 10% of tumor cells were immunoreactive. The association between APAF-1 expression and tumor response was made using the chi-square test.

RESULTS

Forty-four tumors (43%) were positive for APAF-1. Thirty tumors had complete pathologic tumor regression after preoperative radiotherapy. Of these, 18 tumors were positive for APAF-1. A partial response occurred in 35 tumors. Eighteen tumors (51%) were positive for the protein. Only 8 of 29 nonresponsive tumors (28%) were immunoreactive for APAF-1. A significant association was found between complete tumor regression and positive APAF-1 status (P = 0.018). APAF-1 expression in partially responsive tumors was significantly greater than in nonresponsive tumors (P = 0.03).

CONCLUSIONS

APAF-1 expression in pretreatment rectal tumor biopsy specimens may be useful as a predictive marker of response to preoperative radiotherapy in patients with rectal carcinoma.

Three-dimensional Structure of a Double Apoptosome Formed by the Drosophila Apaf-1 Related Killer

The Drosophila Apaf-1 related killer (Dark) forms an apoptosome that activates Dronc, an apical procaspase in the intrinsic cell death pathway. To study this process, we assembled a large Dark complex in the presence of dATP. Remarkably, we found that cytochrome c was not required for assembly and when added, cytochrome c did not bind to the Dark complex. We then determined a 3D structure of the Dark complex at 18.8A resolution using electron cryo-microscopy and single particle methods. In the structure, eight Dark subunits form a wheel-like particle and two of these rings associate face-to-face. In contrast, Apaf-1 forms a single ring that is comprised of seven subunits and each Apaf-1 binds a molecule of cytochrome c. We then used relevant crystal structures to model the Dark complex. This analysis shows that a single Dark ring and the Apaf-1 apoptosome share many key features. When taken together, the data suggest that a single ring in the Dark complex may represent the Drosophila apoptosome. Thus, our analysis provides a domain model of this complex and gives insights into its function.

Suppression of mammary carcinoma growth by retinoic acid: proapoptotic genes are targets for retinoic acid receptor and cellular retinoic acid-binding protein II signaling

Retinoic acid (RA) displays pronounced anticarcinogenic activities in several types of cancer. Whereas the mechanisms that underlie this activity remain incompletely understood, tumor suppression by RA is believed to emanate primarily from its ability to regulate transcription of multiple target genes. Here, we investigated molecular events through which RA inhibits the growth of MCF-7 mammary carcinoma cells, focusing on the involvement of the two proteins that mediate transcriptional activation by RA, the nuclear hormone receptor retinoic acid receptor (RAR) and the cellular retinoic acid-binding protein (CRABP) II, in this process. RA treatment of MCF-7 cells did not affect cell cycle distribution but triggered pronounced apoptosis. Accordingly, expression array analyses revealed that RA induces the expression of several proapoptotic genes, including caspase 7 and caspase 9. Whereas caspase 7 is an indirect responder to RA signaling, caspase 9 is a novel direct target for RAR, and it harbors a functional retinoic acid response element in its second intron. In agreement with the known role of CRABP-II in enhancing the transcriptional activity of RAR, the binding protein augmented RA-induced up-regulation of caspase 9, cooperated with RA in activating both caspase 7 and 9, and amplified the ability of RA to trigger apoptosis. Surprisingly, the data indicate that CRABP-II also displays proapoptotic activities on its own. Specifically, overexpression of CRABP-II, in the absence of RA, up-regulated the expression of Apaf1 and triggered caspase 7 and caspase 9 cleavage. These observations suggest that, in addition to its known role in direct delivery of RA to RAR, CRABP-II may have an additional, RA-independent, function.

Regulation of neuronal P53 activity by CXCR 4

Abnormal activation of CXCR 4 during inflammatory/infectious states may lead to neuronal dysfunction or damage. The major goal of this study was to determine the coupling of CXCR 4 to p53-dependent survival pathways in primary neurons. Neurons were stimulated with the HIV envelope protein gp120(IIIB) or the endogenous CXCR 4 agonist, SDF-1 alpha. We found that gp120 stimulates p53 activity and induces expression of the p53 pro-apoptotic target Apaf-1 in cultured neurons. Inhibition of CXCR 4 by AMD 3100 abrogates the effect of gp120 on both p53 and Apaf-1. Moreover, gp120 neurotoxicity is markedly reduced by the p53-inhibitor, pifithrin-alpha. The viral protein also regulates p53 phosphorylation and expression of other p53-responsive genes, such as MDM 2 and p21. Conversely, SDF-1 alpha, which can promote neuronal survival, increases p53 acetylation and p21 expression in neurons. Thus, the stimulation of different p53 targets could be instrumental in determining the outcome of CXCR 4 activation on neuronal survival in neuro-inflammatory disorders.

Polyamines and apoptosis

The natural polyamines putrescine, spermidine and spermine are in multiple ways involved in cell growth and the maintenance of cell viability. In the course of the last 15 years more and more evidence hinted also at roles in gene regulation. It is therefore not surprising that the polyamines are involved in events inherent to genetically programmed cell death. Following inhibition of ornithine decarboxylase, a key step in polyamine biosynthesis, numerous links have been identified between the polyamines and apoptotic pathways. Examples of activation and prevention of apoptosis due to polyamine depletion are known for several cell lines. Elevation of polyamine concentrations may lead to apoptosis or to malignant transformation. These observations are discussed in the present review, together with possible mechanisms of action of the polyamines. Contradictory results and incomplete information blur the picture and complicate interpretation. Since, however, much interest is focussed at present on all aspects of programmed cell death, a considerable progress in the elucidation of polyamine functions in apoptotic signalling pathways is expected, even though enormous difficulties oppose pinpointing specific interactions of the polyamines with pro- and anti-apoptotic factors. Such situation is quite common in polyamine research.

Expression of apoptosome pathway-related transcripts in non-small cell lung cancer

PURPOSE

Tumour cells killing by cytotoxic therapies largely depends on triggering the intrinsic apoptosome-mediated caspase activation pathway but it had never been evaluated whether the expression of transcripts encoding the core components of apoptosome pathway is altered in non-small cell lung carcinoma (NSCLC).

METHODS

We investigated the expression status of several apoptosome pathway-related transcripts including Apaf-1, procaspase-9, -3, -6, -7 and Smac in tumour and lung tissue samples from 65 surgically treated NSCLC patients and in 10 NSCLC cell lines with using real time RT-PCR.

RESULTS

NSCLC tissues and cell lines showed significantly increased expression of procaspase-9, -3, -6 and Smac mRNAs as compared to the lungs and expression of these transcripts was simultaneously upregulated in a subset of NSCLCs belonging to different histopathological type, grade and stage categories. The expression of procaspase-7 mRNA in NSCLC tissues and cell lines and lungs was not significantly different. By contrast, the expression of Apaf-1 mRNA was frequently downregulated in the tumours as compared to matched lungs. Nevertheless, the examined NSCLC cell lines showed significantly higher expression of Apaf-1 mRNA than the lungs. The expression of Apaf-1, procaspase-9 and -6 mRNAs was higher in lung adenocarcinomas as compared to squamous cell lung carcinomas but the expression levels of the studied apoptosome pathway-related transcripts in the tumours were independent of tumour's grade and stage.

CONCLUSIONS

The results of the present study suggest that there is a subgroup of NSCLCs, which may be intrinsically primed for apoptosis through upregulated expression of transcripts encoding the apoptosome pathway components.

Expression of Apaf-1 in cervical cancer correlates with lymph node metastasis but not with intratumoral hypoxia

OBJECTIVES

The aim of this study was to investigate the expression of the proapoptotic protein Apaf-1 in cervical cancers. Moreover, we studied its correlation to intratumoral pO(2) and to clinico-pathological parameters.

METHODS

86 patients with cervical cancer were subjected to intratumoral pO(2) measurement with the Eppendorf electrode. From these patients, cervical cancer tissue was used for immunohistochemistry with an anti-Apaf-1 antibody.

RESULTS

Apaf-1 is expressed in cervical cancer. Cervical cancers with strong or moderate Apaf-1 expression had significantly less lymph node metastases at time of surgery than tumors with weak or negative Apaf-1 expression (P = 0.022). There was no significant correlation between Apaf-1 expression and intratumoral pO(2), pT stage, FIGO stage, lymphovascular space involvement, and grade.

CONCLUSIONS

Loss of Apaf-1 expression may represent a marker of aggressive tumor behavior since it correlates significantly with the occurrence of lymph node metastasis in cervical cancer.

Dying a thousand deaths: redundant pathways from different organelles to apoptosis and necrosis

Cell death is an essential event in normal life and development, as well as in the pathophysiological processes that lead to disease. Although the literature on cell death has grown enormously in size and complexity, a pattern has emerged that each of several distinct organelles (plasma membrane, mitochondrion, nucleus, endoplasmic reticulum, lysosome) gives rise to signals that induce cell death. Most often these signals converge on mitochondria to initiate a common pathway to either caspase-dependent apoptosis or ATP depletion-dependent necrosis. This brief overview emphasizes the multiple and often redundant pathways between different organelles that lead ultimately to a cell's demise.

Receptorial and mitochondrial apoptotic pathways in normal and neoplastic human endometrium

Under normal conditions, in human endometrium, apoptotic and antiapoptotic factors play an important role in tissue homeostasis. Abnormalities of apoptosis, a process implicated in several events in the reproductive organs, may contribute to neoplastic transformation. The present study aimed to investigate the involvement of both the receptorial and the mitochondrial pathways of apoptosis in normal endometrium and in endometrial carcinoma, by measuring caspase-3 and caspase-8 activities and cytosolic cytochrome c levels. Twelve endometrial carcinomas and nine normal endometrial specimens (four in mild proliferative phase, five in late secretory phase) were included in this study. Cytosolic fractions, obtained by differential centrifugation of tissue homogenates, were analyzed for caspase-3 and caspase-8 activities, as well as for cytochrome c content. Caspase-8 activity in normal secretory phase endometrium was higher than that in the proliferative phase and in the endometrial carcinoma. Moreover, higher cytochrome c levels were detected in endometrial carcinoma with respect to normal secretive endometrium. No significant differences were found in caspase-3 activity between normal and pathologic endometrium. The results obtained suggest that in normal endometrium, apoptosis takes place through the activation of both receptorial and mitochondrial pathways. Defects in both these pathways may contribute to the development of endometrial carcinoma.

Apoptosome inactivation rescues proneural and neural cells from neurodegeneration

Deficiency of the apoptosome component Apaf1 leads to accumulation of supernumerary brain cells in mouse embryos. We observed that neural precursor cells (NPCs) in Apaf1(-/-) embryos escape programmed cell death, proliferate and retain their potential to differentiate. To evaluate the circumstances of Apaf1(-/-) NPC survival and investigate their fate under neurodegenerative conditions, we established cell lines of embryonic origin (ETNA). We found that Apaf1(-/-) NPCs resist common apoptotic stimuli and neurodegenerative inducers such as amyloid-beta peptide (typical of Alzheimer's disease) and mutant G93A superoxide dismutase 1 (typical of familial amyotrophic lateral sclerosis). Similar results were obtained in Apaf1(-/-) primary cells. When death is prevented by Apaf1 deficiency, cytochrome c is released from mitochondria and rapidly degraded by the proteasome, but mitochondria remain intact. Under these conditions, neither activation by cleavage of initiator caspases nor release of alternative apoptotic inducers from mitochondria takes place. In addition, NPCs can still differentiate, as revealed by neurite outgrowth and expression of differentiation markers. Our findings imply that the mitochondrion/apoptosome pathway is the main route of proneural and neural cells to death and that its inhibition prevents them from dismantling in neurodegenerative conditions. Indeed, the ETNA cell model is ideally suited for exploring the potential of novel cell therapies for the treatment of human neurodegenerations.

Tumor necrosis factor death receptor signaling cascade is required for amyloid-beta protein-induced neuron death

Tumor necrosis factor type I receptor (TNFRI), a death receptor, mediates apoptosis and plays a crucial role in the interaction between the nervous and immune systems. A direct link between death receptor activation and signal cascade-mediated neuron death in brains with neurodegenerative disorders remains inconclusive. Here, we show that amyloid-beta protein (Abeta), a major component of plaques in the Alzheimer's diseased brain, induces neuronal apoptosis through TNFRI by using primary neurons overexpressing TNFRI by viral infection or neurons from TNFRI knock-out mice. This was mediated via alteration of apoptotic protease-activating factor (Apaf-1) expression that in turn induced activation of nuclear factor kappaB (NF-kappaB). Abeta-induced neuronal apoptosis was reduced with lower Apaf-1 expression, and little NF-kappaB activation was found in the neurons with mutated Apaf-1 or a deletion of TNFRI compared with the cells from wild-type (WT) mice. Our studies suggest a novel neuronal response of Abeta, which occurs through a TNF receptor signaling cascade and a caspase-dependent death pathway.

Caspase activity inhibition delays programmed spermatogenic cell death in vitro

Programmed cell death or apoptosis was analyzed in rat Sertoli-spermatogonial cell cocultures prepared from 2-9 day old rats using time-lapse video microscopy, a cell viability fluorescence microscopy assay, immunocytochemical markers, and cell-permeable caspase inhibitory peptides with reversible and irreversible effects. We show that apoptosis can initially affect a single member of a spermatogonial cell cohort and that single non-viable spermatogonial cells can remain conjoined to viable spermatogonial cells. The integrity of the cytoskeletal F-actin network and the presence on Bcl-2 immunoreactivity are valuable markers of spermatogonial cell viability. Apoptotic bodies released into the culture medium are generally eliminated after culture medium replenishment; however, spermatogonial apoptotic cell remnants can be taken up by Sertoli cells, which are known to represent a phagocytic somatic population within the seminiferous epithelium. Cell permeable caspase-1 and caspase-4 inhibitory peptides with reversible and irreversible action were supplemented to a serum-free hormone-growth factor-supplemented medium. In the absence of the caspase inhibitory peptide, the viability of spermatogonial cells decreases gradually with time in coculture. However, the addition of caspase inhibitory peptides causes a significant accumulation of spermatogenic cells per unit surface area. Although inhibition of caspases, the executors of spermatogonial cell death, results in a substantial increase of spermatogonial cells in the cocultures, it remains to be determined what the differentiation potential of caspase-inhibited spermatogonial cell cohorts is.