Cell death in the third millennium

Mechanism and treatment of α-amanitin poisoning

Amanita poisoning has a high mortality rate. The α-amanitin toxin in Amanita is the main lethal toxin. There is no specific detoxification drug for α-amanitin, and the clinical treatment mainly focuses on symptomatic and supportive therapy. The pathogenesis of α-amanitin mainly includes: α-amanitin can inhibit the activity of RNA polymeraseII in the nucleus, including the inhibition of the largest subunit of RNA polymeraseII, RNApb1, bridge helix, and trigger loop. In addition, α-amanitin acts in vivo through the enterohepatic circulation and transport system. α-Amanitin can cause the cell death. The existing mechanisms of cell damage mainly focus on apoptosis, oxidative stress, and autophagy. In addition to the pathogenic mechanism, α-amanitin also has a role in cancer treatment, which is the focus of current research. The mechanism of action of α-amanitin on the body is still being explored.

A cell's agony of choice: how to cross the Styx? : From morphological to molecular approaches to disclose its decision

The original “apoptosis–necrosis” concept was based on morphology and (patho)physiological conditions of the occurrence of cell death: (1) apoptosis, with nuclear and cytoplasmic condensation/fragmentation prominent, exclusion of autolysis, considered to result from coordinated self-destruction of a cell; (2) necrosis, with cell lysis prominent, caused by violent environmental perturbation leading to collapse of internal homeostasis. This suggestion initiated a controversial discussion within the scientific community and it soon became clear that the “apoptosis–necrosis dichotomy” was not generally applicable. Nowadays, there is sufficient evidence that cells may activate diverse suicide pathways, thereby allowing a flexible response to environmental changes, either physiological or pathological. The present paper commemorates electron microscopic and cytochemical studies on cell death of cultured human mammary carcinoma cells performed by Adi Ellinger, adding a significant contribution to recognize that autophagy can be involved in regulated cell death, thereby challenging the apoptosis–necrosis dichotomy still predominant in the 1990s.

(99m)Tc-Annexin A5 quantification of apoptotic tumor response: a systematic review and meta-analysis of clinical imaging trials

PURPOSE

(99m)Tc-Annexin A5 has been used as a molecular imaging probe for the visualization, characterization and measurement of apoptosis. In an effort to define the quantitative (99m)Tc-annexin A5 uptake criteria that best predict tumor response to treatment, we performed a systematic review and meta-analysis of the results of all clinical imaging trials found in the literature or publicly available databases.

METHODS

Included in this review were 17 clinical trials investigating quantitative (99m)Tc-annexin A5 (qAnx5) imaging using different parameters in cancer patients before and after the first course of chemotherapy and/or radiation therapy. Qualitative assessment of the clinical studies for diagnostic accuracy was performed using the QUADAS-2 criteria. Of these studies, five prospective single-center clinical trials (92 patients in total) were included in the meta-analysis after exclusion of one multicenter clinical trial due to heterogeneity. Pooled positive predictive values (PPV) and pooled negative predictive values (NPV) (with 95% CI) were calculated using Meta-Disc software version 1.4.

RESULTS

Absolute quantification and/or relative quantification of (99m)Tc-annexin A5 uptake were performed at baseline and after the start of treatment. Various quantitative parameters have been used for the calculation of (99m)Tc-annexin A5 tumor uptake and delta (Δ) tumor changes post-treatment compared to baseline including: tumor-to-background ratio (TBR), ΔTBR, tumor-to-noise ratio, relative tumor ratio (TR), ΔTR, standardized tumor uptake ratio (STU), ΔSTU, maximum count per pixel within the tumor volume (Cmax), Cmax%, absolute ΔU and percentage (ΔU%), maximum ΔU counts, semiquantitative visual scoring, percent injected dose (%ID) and %ID/cm(3). Clinical trials investigating qAnx5 imaging have included patients with lung cancer, lymphoma, breast cancer, head and neck cancer and other less common tumor types. In two phase I/II single-center clinical trials, an increase of ≥25% in uptake following treatment was considered a significant threshold for an apoptotic tumor response (partial response, complete response). In three other phase I/II clinical trials, increases of ≥28%, ≥42% and ≥47% in uptake following treatment were found to be the mean cut-off levels in responders. In a phase II/III multicenter clinical trial, an increase of ≥23% in uptake following treatment was found to be the minimum cut-off level for a tumor response. In one clinical trial, no significant difference in (99m)Tc-annexin A5 uptake in terms of %ID was found in healthy tissues after chemotherapy compared to baseline. In two other clinical trials, intraobserver and interobserver measurements of (99m)Tc-annexin A5 tumor uptake were found to be reproducible (mean difference <5%, kappa =  0.90 and 0.82, respectively) and to be highly correlated with treatment outcome (Spearman r = 0.99, p < 0.0001). The meta-analysis demonstrated a pooled positive PPV of 100% (95% CI 92 - 100%) and a pooled NPV of 70% (95% CI 55 - 82%) for prediction of a tumor response after the first course of chemotherapy and/or radiotherapy in terms of ΔU%. In a symmetric sROC analysis, the AUC was 0.919 and the Q* index was 85.21 %.

CONCLUSION

Quantitative (99m)Tc-annexin A5 imaging has been investigated in clinical trials for the assessment of apoptotic tumor responses. This meta-analysis showed a high pooled PPV and a moderate pooled NPV with ΔU cut-off values ranging between 20% and 30%. Standardization of quantification and harmonization of results are required for high-quality clinical research. A standardized uptake value score (SUV, ΔSUV) using quantitative SPECT/CT imaging may be a promising approach to the simple, reproducible and semiquantitative assessment of apoptotic tumor changes.

Triazole analog 1-(1-benzyl-5-(4-chlorophenyl)-1H-1,2,3-triazol-4-yl)-2-(4-bromophenylamino)-1-(4-chlorophenyl)ethanol induces reactive oxygen species and autophagy-dependent apoptosis in both in vitro and in vivo breast cancer models

Autophagy is considered as an important cell death mechanism that closely interacts with other common cell death programs like apoptosis. Critical role of autophagy in cell death makes it a promising, yet challenging therapeutic target for cancer. We identified a series of 1,2,3-triazole analogs having significant breast cancer inhibition property. Therefore, we attempted to study whether autophagy and apoptosis were involved in the process of cancer cell inhibition. The lead molecule, 1-(1-benzyl-5-(4-chlorophenyl)-1H-1,2,3-triazol-4-yl)-2-(4-bromophenylamino)-1-(4-chlorophenyl)ethanol (T-12) induced significant cell cycle arrest, mitochondrial membrane depolarization, apoptosis and autophagy in MCF-7 and MDA-MB-231 cells. T-12 increased reactive oxygen species and its inhibition by N-acetyl-L-cysteine protected breast cancer cells from autophagy and apoptosis. Autophagy inhibitor, 3-methyladenine abolished T-12 induced apoptosis, mitochondrial membrane depolarization and reactive oxygen species generation. This suggested that T-12 induced autophagy facilitated cell death rather than cell survival. Pan-caspase inhibition did not abrogate T-12 induced autophagy, suggesting that autophagy precedes apoptosis. In addition, T-12 inhibited cell survival pathway signaling proteins, Akt, mTOR and Erk1/2. T-12 also induced significant regression of tumor with oral dose of as low as 10mg/kg bodyweight in rat mammary tumor model without any apparent toxicity. In presence of reactive oxygen species inhibitor (N-acetyl-L-cysteine) and autophagy inhibitor (chloroquine), T-12 induced tumor regression was significantly decreased. In conclusion, T-12 is a potent inducer of autophagy-dependent apoptosis in breast cancer cells both in vitro and in vivo and can serve as an important lead in development of new anti-tumor therapy.

Long term induction by pterostilbene results in autophagy and cellular differentiation in MCF-7 cells via ROS dependent pathway

This study shows the effect of pterostilbene on intracellular neutral lipid accumulation in MCF-7 breast cancer cells leading to growth arrest and autophagy. On exposing the breast cancer cells with 30 μM pterostilbene for 72 h there was almost 2-folds increase in neutral lipids and triglycerides. Also the phytochemical caused a 4-folds increase in the expression of adipogenic differentiation marker c/EBPα. Further, pterostilbene inhibited 3β-hydroxylsterol-Δ(7)-reductase, the enzyme which catalyzes the last step conversion of 7-dehydrocholesterol to cholesterol, and thereby causes the intracellular accumulation of the former sterol. These results were associated with over-expression of oxysterol binding protein homologue and liver X receptor (LXR) by ~7-folds. Pterostilbene also caused a simultaneous increase in the expression autophagic marker proteins Beclin 1 and LC3 II (microtubule-associated protein 1 light chain 3) by approximately 6-folds, which leads to an alternative pathway of autophagy. These effects were observed in association with the loss of mitotic and metastatic potential of MCF-7 cells which was abolished in the presence of catalase (ROS scavenger) or 3MA (autophagic inhibitor). Thus the present data shows that the long term exposure to pterostilbene causes growth arrest in MCF-7 cells which may be due to differentiation of the mammary carcinoma cells into normal epithelial cell like morphology and activation of autophagy.

Cytotoxicity and genotoxicity reporter systems based on the use of mammalian cells

With the dramatic increase in the number of new agents arising from the chemical, pharmaceutical, and agricultural industries, there is an urgent need to develop assays for rapid evaluation of potential risks to man and environment. The panel of conventional tests used for cytotoxicity and genotoxicity and the strategies to progress from small scale assays to high content screening in toxicology are discussed. The properties of components necessary as sensors and reporters for new reporter assays, and the application of genetic strategies to design assays are reviewed. The concept of cellular reporters is based on the use of promoters of chemical stress-regulated genes ligated to a suitable luminescent or fluorescent reporter gene. Current reporter assays designed from constructs transferred into suitable cell lines are presented.

Treatment of PC-3 and DU145 prostate cancer cells by prenylflavonoids from hop (Humulus lupulus L.) induces a caspase-independent form of cell death

Xanthohumol (X), isoxanthohumol (IX), 8-prenylnaringenin (8PN) and 6-prenylnaringenin (6PN), prenylflavonoids from hop (Humulus lupulus L.), were investigated for their cytotoxicity and the mechanism by which they exert cell death when incubated with prostate cancer cell lines PC-3 and DU145. All compounds induced cell death in the absence of caspase-3 activation and typical apoptotic morphological features. The general pan-caspase inhibitor zVAD-fmk could not protect this form of cell death. In addition, the formation of vacuoles was observed in PC-3 cells treated with IX and 6PN, and in DU145 treated with IX, 8PN and 6PN, which could suggest the induction of autophagy and consequent cell death. The results indicate that hop-derived prenylflavanones (IX, 8PN, 6PN), but not prenylchalcones (X) induce a caspase-independent form of cell death, suggested to be autophagy. Therefore, IX, 8PN and 6PN appear to be promising candidates for further investigation in prostate anticancer therapy.

Cardiomyocyte death and renewal in the normal and diseased heart

During post-natal maturation of the mammalian heart, proliferation of cardiomyocytes essentially ceases as cardiomyocytes withdraw from the cell cycle and develop blocks at the G0/G1 and G2/M transition phases of the cell cycle. As a result, the response of the myocardium to acute stress is limited to various forms of cardiomyocyte injury, which can be modified by preconditioning and reperfusion, whereas the response to chronic stress is dominated by cardiomyocyte hypertrophy and myocardial remodeling. Acute myocardial ischemia leads to injury and death of cardiomyocytes and nonmyocytic stromal cells by oncosis and apoptosis, and possibly by a hybrid form of cell death involving both pathways in the same ischemic cardiomyocytes. There is increasing evidence for a slow, ongoing turnover of cardiomyocytes in the normal heart involving death of cardiomyocytes and generation of new cardiomyocytes. This process appears to be accelerated and quantitatively increased as part of myocardial remodeling. Cardiomyocyte loss involves apoptosis, autophagy, and oncosis, which can occur simultaneously and involve different individual cardiomyocytes in the same heart undergoing remodeling. Mitotic figures in myocytic cells probably represent maturing progeny of stem cells in most cases. Mitosis of mature cardiomyocytes that have reentered the cell cycle appears to be a rare event. Thus, cardiomyocyte renewal likely is mediated primarily by endogenous cardiac stem cells and possibly by blood-born stem cells, but this biological phenomenon is limited in capacity. As a consequence, persistent stress leads to ongoing remodeling in which cardiomyocyte death exceeds cardiomyocyte renewal, resulting in progressive heart failure. Intense investigation currently is focused on cell-based therapies aimed at retarding cardiomyocyte death and promoting myocardial repair and possibly regeneration. Alteration of pathological remodeling holds promise for prevention and treatment of heart failure, which is currently a major cause of morbidity and mortality and a major public health problem. However, a deeper understanding of the fundamental biological processes is needed in order to make lasting advances in clinical therapeutics in the field.

Dynamic effects of autophagy on arsenic trioxide-induced death of human leukemia cell line HL60 cells

AIM

To evaluate the contribution of an autophagic mechanism to the As2O3- induced death of human acute myeloid leukaemia cell line HL60 cells.

METHODS

The growth inhibition of HL60 cells induced by As2O3 was assessed with 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide colorimetric assay. The activation of autophagy was determined with monodansylcadaverine labeling and transmission electron microscope. The role of autophagy in the As2O3-induced death of HL60 cells was assessed using autophagic and lysosomal inhibitors. Immunofluorescence, flow cytometry, and Western blot analysis were used to study the apoptotic and autophagic mechanisms.

RESULTS

After treatment with As2O3, the proliferation of HL60 cells was significantly inhibited and the formation of autophagosomes increased. The blockade of autophagy maturation with the autophagy-specific inhibitor 3-methyladenine (3-MA) or the lysosome-neutralizing agent NH4Cl 1 h before As2O3 potentiated the As2O3-induced death of HL60 cells. In contrast, 3-MA attenuated As2O3-induced death when administered 30 min after As2O3. 3-MA and NH4Cl also inhibited As2O3-induced upregulation of microtubule-associated protein 1 light chain 3, the protein required for autophagy in mammalian cells. Following As2O3, lysosomes were activated as indicated by increased levels of cathepsins B and L. The apoptotic response of HL60 cells to As2O3 was suggested by the collapse of mitochondrial membrane potential, release of cytochrome c from mitochondria, and the activation of caspase-3. Pretreatment with 3-MA prior to As2O3 amplified these apoptotic signals, while posttreatment with 3-MA 30 min after As2O3 attenuated the apoptotic pathways.

CONCLUSION

Autophagy plays complex roles in the As2O3-induced death of HL60 cells; it inhibits As2O3-induced apoptosis in the initiation stage, but amplifies the As2O3-mediated apoptotic program if it is persistently activated.

Live and let die: manipulation of host hepatocytes by exoerythrocytic Plasmodium parasites

The generation of rodent Plasmodium strains expressing fluorescent proteins in all life cycle stages has had a big impact on malaria research. With this tool in hand, for the first time it was possible to follow in real time by in vivo microscopy the infection route of Plasmodium sporozoites transmitted to the mammalian host by Anopheles mosquitoes. Recently, this work has been extended to the analysis of both hepatocyte infection by Plasmodium sporozoites, as well as liver merozoite transport into blood vessels. The stunning results of these studies have considerably changed our understanding of hepatocyte invasion and parasite liberation. Here, we describe the most important findings of the last years and in addition, we elaborate on the molecular events during the intracellular development of Plasmodium exoerythrocytic forms that give rise to erythrocyte infecting merozoites.

Autophagy is involved in T cell death after binding of HIV-1 envelope proteins to CXCR4

HIV-1 envelope glycoproteins (Env), expressed at the cell surface, induce apoptosis of uninfected CD4+ T cells, contributing to the development of AIDS. Here we demonstrate that, independently of HIV replication, transfected or HIV-infected cells that express Env induced autophagy and accumulation of Beclin 1 in uninfected CD4+ T lymphocytes via CXCR4. The same phenomena occurred in a T cell line and in transfected HEK.293 cells that expressed both wild-type CXCR4 and a truncated form of CD4 that is unable to bind the lymphocyte-specific protein kinase Lck. Env-mediated autophagy is required to trigger CD4+ T cell apoptosis since blockade of autophagy at different steps, by either drugs (3-methyladenine and bafilomycin A1) or siRNAs specific for Beclin 1/Atg6 and Atg7 genes, totally inhibited the apoptotic process. Furthermore, CD4+ T cells still underwent Env-mediated cell death with autophagic features when apoptosis was inhibited. These results suggest that HIV-infected cells can induce autophagy in bystander CD4+ T lymphocytes through contact of Env with CXCR4, leading to apoptotic cell death, a mechanism most likely contributing to immunodeficiency.

Expression of cell kinetics and death during monocyte-macrophage differentiation: effects of Actinomycin D and Vinblastine treatments

The different effects of two cytostatic drugs, Actinomycin D and Vinblastine, during macrophage-like differentiation induced in THP-1 monocytic cell line by phorbol ester phorbol 12-myristate 13-acetate (PMA) (6, 30, and 60 nM), were studied by morpho-cytochemical approaches. In PMA-unstimulated monocytic cells, the cytostatic effects of Actinomycin D (an antimetabolic drug) were characterized by a drastic reduction of the G2/M cells accompanied by dramatic death of the G1 cells; on the contrary, Vinblastine (a microtubule-depolymerizating drug) induced an accumulation of the G2/M cells with the appearance of aneugenic micronuclei and scarce cell death mainly from the G1 cells. After 60 nM PMA stimulation, the culture was mostly composed by macrophagic cells characterized by low proliferation and the appearance of mono-/binucleated polyploid cells; in this condition, the cytotoxicity of the two drugs, more effective for Vinblastine, induced cell death in the different ploidy classes (2c, 4c, 8c). Cell death appeared to be of apoptotic nature, but with some morpho-phenotypic differences due to the action mechanism of the drugs and dependent on cell culture growth and differentiation. As a consequence of the different block-action of the two drugs on the cell cycle phases and in relation to the different subcellular targets, the effects changed during the transition from not-adhering/proliferating monocytes to adhering/low-proliferating differentiated macrophages.

Transrenal DNA testing: progress and perspectives

Transrenal DNA (Tr-DNA) is a recently discovered class of extracellular urinary DNA that originates from cells dying throughout the body. Postapoptotic DNA is known to appear in the circulating plasma, but it is now recognized that a portion of these fragments cross the kidney barrier and appear in urine in the form of 150-200-bp fragments. Tr-DNA containing fetal sequences has been isolated from the urine of pregnant women, tumor-specific mutations have been detected in Tr-DNA from patients with colon and pancreatic tumors, and donor DNA has been found in Tr-DNA isolated from recipient urine. Furthermore, proviral HIV DNA, bacterial and parasite DNA sequences have been detected in Tr-DNA from infected patients. Potential applications of Tr-DNA-based tests cover a very broad area of molecular diagnostics and genetic testing, including prenatal detection of inherited diseases, tumor diagnostics and therapeutic monitoring and detection of infectious agents. The Tr-DNA test is expected to have utility in treatment monitoring, transplantation monitoring, drug development and broad public health screening, where a noninvasive, common-platform diagnostic technology has particular value. This review describes some of the highlights of Tr-DNA technology applications, advantages over existing technologies and potential problems anticipated in test development.

A novel paraptosis pathway involving LEI/L-DNaseII for EGF-induced cell death in somato-lactotrope pituitary cells

We have recently reported that EGF triggers an original form of cell death in pituitary cell line (GH4C1) with a phenotype sharing some characteristics of both apoptosis (internucleosomal DNA fragmentation) and paraptosis (caspase-independence and cytoplasmic vacuolization). However, the endonuclease involved in EGF-induced DNA fragmentation has not been assessed so far. In the present work we therefore further explored the putative paraptosis involvement in EGF-induced cell death and asked whether L-DNaseII might be involved. Indeed, this endonuclease is known to mediate internucleosomal DNA fragmentation in caspase independent manner. Our Western blot, immunocytochemistry and enzymatic measurement assays show that EGF triggers a cleavage of Leukocyte Elastase Inhibitor (LEI) precursor into L-DNaseII, its subsequent enzymatic activation and nuclear translocation thus pointing to the involvement of this endonuclease pathway in caspase-independent DNA fragmentation. In addition, EGF-induced cell death can be blocked by paraptosis inhibitor AIP-1/Alix, but not with its anti-apoptotic C-terminal fragment (Alix-CT). Altogether these data suggest that EGF-induced cell death defines a novel, L-DNaseII-mediated form of paraptosis.

Pathways of myocyte death: implications for development of clinical laboratory biomarkers

The recognition that cardiac myocytes die by multiple mechanisms and thus substantially affect ventricular remodeling in diseased human hearts supports the concept of ongoing myocyte death in the progression of heart failure and constitutes the basis of this review. In addition, based on the pathophysiology of myocardial cell deaths, the present study emphasizes that currently methodologies, although with some inherent limitations, are available to recognize and measure quantitatively the contribution of myocyte cell death to the progression of the pathologic state of the heart. Our own studies show that application of such methodologies including modern microscopy techniques and the use of different molecular and immunohistochemical markers may generate the consensus that myocyte cell death is a quantifiable parameter in the normal and pathological human heart. The present study also demonstrates that myocyte cell death, apoptotic, oncotic or autophagic in nature, has to be regarded as an additional critical variable of the multifactorial events implicated in the alterations of cardiac anatomy and myocardial structure of the diseased human heart.

Cell death independent of caspases: a review

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

Apoptosis, autophagy, and more

Cell death has been subdivided into the categories apoptosis (Type I), autophagic cell death (Type II), and necrosis (Type III). The boundary between Type I and II has never been completely clear and perhaps does not exist due to intrinsic factors among different cell types and the crosstalk among organelles within each type. Apoptosis can begin with autophagy, autophagy can end with apoptosis, and blockage of caspase activity can cause a cell to default to Type II cell death from Type I. Furthermore, autophagy is a normal physiological process active in both homeostasis (organelle turnover) and atrophy. "Autophagic cell death" may be interpreted as the process of autophagy that, unlike other situations, does not terminate before the cell collapses. Since switching among the alternative pathways to death is relatively common, interpretations based on knockouts or inhibitors, and therapies directed at controlling apoptosis must include these considerations.

Apoptotic markers in cancer

In cancer, apoptotic processes occur both spontaneously and induced by antitumor therapies. Qualitative and quantitative changes in cancer cell death along with proliferative alterations are essential determinants in the pathogenesis and progression of malignant disease and its responsiveness to therapy. Besides detecting apoptosis by invasive means in tumor tissue, apoptotic products can be quantified in the circulation. Although circulating apoptotic products usually lack organ and tumor specificity, they contribute in the assessment of disease extent or aggressiveness. The ease of drawing blood facilitates the serial measurement of circulating apoptotic markers to monitor antitumor treatment and predict early response to therapy. This review describes the features of apoptotic and necrotic cell death along with the role the balance between the rates of cell death and cell proliferation plays in the progression of malignancy. The intracellular pathways mediating apoptosis are next summarized. The focus then shifts to the apoptotic markers found in the circulation and their diagnostic, prognostic, predictive, and management utility in cancer.

Degradation phase of apoptosis during the early stages of human metanephros development

Apoptosis as a vital process is necessary for human intrauterine development. Not only the induction and course of apoptosis, but engulfment of the apoptotic cells (bodies) were the centre of our interest. Macrophages were detected in the early stages of human intrauterine development and the role of macrophages in the clearance of apoptotic cells in the early stages of human metanephros development was confirmed.

Growth factor deprivation induces an alternative non-apoptotic death mechanism that is inhibited by Bcl2 in cells derived from neural precursor cells

Although apoptosis has been considered the typical mechanism for physiological cell death, presently alternative mechanisms need to be considered. We previously showed that fibroblast growth factor-2 (FGF2) could act as a survival factor for neural precursor cells. To study the death mechanism activated by the absence of this growth factor, we followed the changes in cell morphology and determined cell viability by staining with several dyes after FGF2 removal from mesencephalic neural-progenitor-cell cultures. The changes observed did not correspond to those associated with apoptosis. After 48 h in the absence of FGF2, cells began to develop vacuoles in their cytoplasm, a phenotype that became very obvious 3-5 days later. Double-membrane vacuoles containing cell debris were observed. Vacuolated cells did not stain with either ethidium bromide or trypan Blue, and did not show chromatin condensations. Nonetheless, during the course of culture, vacuolated cells formed aggregates with highly condensed chromatin and detached from the plate. Neural progenitor cells grown in the presence of FGF2 did not display any of those characteristics. The vacuolated phenotype could be reversed by the addition of FGF2. Typical autophagy inhibitors such as 3-MA and LY294002 inhibited vacuole development, whereas a broad-spectrum caspase inhibitor did not. Interestingly, Bcl-2 overexpression retarded vacuole development. In conclusion, we identified a death autophagy-like mechanism activated by the lack of a specific survival factor that can be inhibited by Bcl2. We propose that anti-apoptotic Bcl2 family members are key molecules controlling death activation independently of the cell degeneration mechanism used.

Diphtheria toxin-induced autophagic cardiomyocyte death plays a pathogenic role in mouse model of heart failure

It is still not clear whether loss of cardiomyocytes through programmed cell death causes heart failure. To clarify the role of cell death in heart failure, we generated transgenic mice (TG) that express human diphtheria toxin receptor in the hearts. A mosaic expression pattern of the transgene was observed, and the transgene-expressing cardiomyocytes (17.3% of the total cardiomyocytes) were diffusely scattered throughout the ventricles. Intramuscular injection of diphtheria toxin induced complete elimination of the transgene-expressing cardiomyocytes within 7 days, and approximately 80% of TG showed pathophysiological features characteristic of heart failure and were dead within 14 days. Degenerated cardiomyocytes of the TG heart showed characteristic features indicative of autophagic cell death such as up-regulated lysosomal markers and abundant autophagosomes containing cytosolic organelles like cardiomyocytes of human dilated cardiomyopathy. The heart failure-inducible TG are a useful model for dilated cardiomyopathy, and provided evidence indicating that myocardial cell loss through autophagic cell death plays of a causal role in the pathogenesis heart failure.

Catecholamine-induced apoptosis and necrosis in cardiac and skeletal myocytes of the rat in vivo: the same or separate death pathways?

High levels of catecholamines are myotoxic but the relative amounts of apoptosis and necrosis have not been established in vivo in cardiac and skeletal muscles. Immunohistochemistry was used to detect and quantify myocyte-specific necrosis (myosin antibody in vivo) and apoptosis (caspase-3 antibody in vitro) in the heart and soleus muscles of male Wistar rats that had received single subcutaneous injections of isoprenaline over the range 1 microg to 5 mg [kg body weight (BW)](-1). Peak myocyte apoptosis occurred 3-6 h after, and necrosis 18 h after, a single injection of 5 mg (kg BW)(-1) isoprenaline in vivo. In the heart myocyte death was mediated through the beta1-adrenergic receptor whereas myocyte death in the soleus muscle was mediated through the beta2-adrenergic receptor. Cardiomyocyte death was heterogeneously distributed throughout the heart, being greatest in the left ventricle (LV) subendocardium and peaking close to the apex, but with significantly more necrosis than apoptosis. Extensive co-localization of caspase-3 and myosin labelling was found in the myocytes of both the heart and the slow-twitch soleus muscle. This, together with similar spatial distributions and responses to catecholamine doses, suggests that either caspase-3 activation occurs in necrotic as well as apoptotic myocytes or that a large proportion of apoptotic myocytes progress to secondary necrosis in vivo.

Thinking globally, acting locally: steroid hormone regulation of the dendritic architecture, synaptic connectivity and death of an individual neuron

Steroid hormones act via evolutionarily conserved nuclear receptors to regulate neuronal phenotype during development, maturity and disease. Steroid hormones exert 'global' effects in organisms to produce coordinated physiological responses whereas, at the 'local' level, individual neurons can respond to a steroidal signal in highly specific ways. This review focuses on two phenomena-the loss of dendritic processes and the programmed cell death (PCD) of neurons-that can be regulated by steroid hormones (e.g. during sexual differentiation in vertebrates). In insects such as the moth, Manduca sexta, and fruit fly, Drosophila melanogaster, ecdysteroids orchestrate a reorganization of neural circuits during metamorphosis. In Manduca, accessory planta retractor (APR) motoneurons undergo dendritic loss at the end of larval life in response to a rise in 20-hydroxyecdysone (20E). Dendritic regression is associated with a decrease in the strength of monosynaptic inputs, a decrease in the number of contacts from pre-synaptic neurons, and the loss of a behavior mediated by these synapses. The APRs in different abdominal segments undergo segment-specific PCD at pupation and adult emergence that is triggered directly and cell-autonomously by a genomic action of 20E, as demonstrated in cell culture. The post-emergence death of APRs provides a model for steroid-mediated neuroprotection. APR death occurs by autophagy, not apoptosis, and involves caspase activation and the aggregation and ultracondensation of mitochondria. Manduca genes involved in segmental identity, 20E signaling and PCD are being sought by suppressive subtractive hybridization (SSH) and cDNA microarrays. Experiments utilizing Drosophila as a complementary system have been initiated. These insect model systems contribute toward understanding the causes and functional consequences of dendritic loss and neurodegeneration in human neurological disorders.

Circulating nucleosomes and response to chemotherapy: an in vitro, in vivo and clinical study on cervical cancer patients

It is known that cell-free DNA circulates in plasma/serum of patients with cancer and that part of this DNA circulates as nucleosomes that can be quantified by ELISA. We analyzed the effect of tumor and chemotherapy upon the levels of nucleosomes in vitro, in vivo and in cervical cancer patients. The levels of nucleosomes pre- and post-treatment were correlated with response in 11 patients receiving chemotherapy. Nucleosomes were determined in nude mice treated with or without cisplatin and carrying tumors generated with HeLa cells, and in the cell lysate and supernatant of HeLa cells exposed to cisplatin in culture. In addition, nucleosomes were determined at different time points in patients and in rats receiving chemotherapy. Nucleosomes were higher in patients that controls (1,760 vs. 601, p = 0.0001). After 24 hr of treatment with oxaliplatin and gemcitabine, the levels decreased in 6 patients of whom 5 had response. Nucleosome levels differed between mice xenografted and not xenografted (765 vs. 378, p = 0.001) and between xenografted treated with or without cisplatin (650 vs. 765, p = 0.010), but not in tumor-free animals treated and untreated with cisplatin (378 vs. 379, p = 0.99). In vitro, nucleosomes reached at peak 8 hr in cell lysates to decrease thereafter, whereas in supernatant, levels continued to increase up to 24 hr. Serial determination of nucleosomes in patients showed a rise within 6-12 hr and then a reduction to below the basal at 24 hr. In rats, nucleosomes had no major changes in those receiving oxaliplatin or the triple combination of cisplatin, gemcitabine and paclitaxel as compared to untreated controls. An overdose of this triple combination produced a transient elevation of almost 1,000 AU over the basal. Our results demonstrate that most of circulating nucleosomes originate from the tumor and that chemotherapy produces an early rise most likely due to tumor apoptosis and that nucleosomes are rapidly cleared from circulation. On the contrary, chemotherapy within the therapeutic range of doses has no effect on nucleosome levels in healthy mice and rats. This data suggests that the determination of circulating nucleosomes pre- and post-treatment could be a useful test to predict response to chemotherapy in cancer patients.

Myocytes die by multiple mechanisms in failing human hearts

We tested the hypothesis that myocyte loss in failing human hearts occurs by different mechanisms: apoptosis, oncosis, and autophagic cell death. Explanted hearts from 19 patients with idiopathic dilated cardiomyopathy (EF< or =20%) and 7 control hearts were analyzed. Myocyte apoptosis revealed by caspase-3 activation and TUNEL staining occurred at a rate of 0.002+/-0.0005% (P<0.05 versus control) and oncosis assessed by complement 9 labeling at 0.06+/-0.001% (P<0.05). Cellular degeneration including appearance of ubiquitin containing autophagic vacuoles and nuclear disintegration was present at the ultrastructural level. Nuclear and cytosolic ubiquitin/protein accumulations occurred at 0.08+/-0.004% (P<0.05). The ubiquitin-activating enzyme E1 and the ligase E3 were not different from control. In contrast, ubiquitin mRNA levels were 1.8-fold (P<0.02) elevated, and the conjugating enzyme E2 was 2.3-fold upregulated (P<0.005). The most important finding, however, is the 2.3-fold downregulation of the deubiquitination enzyme isopeptidase-T and the 1.5-fold reduction of the ubiquitin-fusion degradation system-1, which in conjunction with unchanged proteasomal subunit levels and proteasomal activity results in massive storage of ubiquitin/protein complexes and in autophagic cell death. A 2-fold decrease of cathepsin D might be an additional factor responsible for the accumulation of ubiquitin/protein conjugates. It is concluded that in human failing hearts apoptosis, oncosis, and autophagy act in parallel to varying degrees. A disturbed balance between a high rate of ubiquitination and inadequate degradation of ubiquitin/protein conjugates may contribute to autophagic cell death. Together, these different types of cell death play a significant role for myocyte disappearance and the development of contractile dysfunction in failing hearts.

Steroid-triggered programmed cell death of a motoneuron is autophagic and involves structural changes in mitochondria

Neuronal death occurs during normal development and disease and can be regulated by steroid hormones. In the hawkmoth, Manduca sexta, individual accessory planta retractor (APR) motoneurons undergo a segment-specific pattern of programmed cell death (PCD) at pupation that is triggered directly and cell autonomously by the steroid hormone 20-hydroxyecdysone (20E). APRs from abdominal segment six [APR(6)s] die by 48 hours after pupal ecdysis (PE; entry into the pupal stage), whereas APR(4)s survive until adulthood. Cell culture experiments showed previously that 20E acts directly on APRs to trigger PCD, with intrinsic segmental identity determining which APRs die. The APR(6) death pathway includes caspase activation and loss of mitochondrial function. We used transmission electron microscopy to investigate the ultrastructure of APR somata before and during PCD. APR(4)s showed normal ultrastructure at all stages examined, as did APR(6)s until approximately stage PE. During APR(6) death, there was massive accumulation of autophagic bodies and vacuoles, mitochondria became ultracondensed and aggregated into compact clusters, and ribosomes aggregated in large blocks. Nuclear ultrastructure remained normal, without chromatin condensation, until the nuclear envelope fragmented late in the death process. Light microscopic immunocytochemistry showed that dying APR(6)s were TUNEL-positive, which is diagnostic of fragmented DNA. These observations indicate that the steroid-induced, caspase-dependent, cell-autonomous PCD of APR(6)s is autophagic, not apoptotic, and support an early role for mitochondrial alterations during PCD. This system permits the study of neuronal death in response to its bona fide developmental signal, the rise in a steroid hormone.

Susceptibility of lysosomes to rupture is a determinant for plasma membrane disruption in tumor necrosis factor alpha-induced cell death

Since a release of intracellular contents can induce local inflammatory responses, mechanisms that lead to loss of plasma membrane integrity in cell death are important to know. We showed previously that deficiency of the plasma membrane Ca2+ ATPase 4 (PMCA4) in L929 cells impaired tumor necrosis factor alpha (TNF-alpha)-induced enlargement of lysosomes and reduced cell death. The lysosomal changes can be determined by measuring the total volume of intracellular acidic compartments per cell (VAC), and we show here that inhibition of the increase in VAC due to PMCA4 deficiency not only reduced cell death but also converted TNF-alpha-induced cell death from a process involving disruption of the plasma membrane to a cell demise with a nearly intact plasma membrane. The importance of the size of lysosomes in determining plasma membrane integrity during cell death was supported by the observations that chemical inhibitors that reduce VAC also reduced the plasma membrane disruption induced by TNF-alpha in wild-type L929 cells, while increases in VAC due to genetic mutation, senescence, cell culture conditions, and chemical inhibitors all changed the morphology of cell death from one with an originally nearly intact plasma membrane to one with membrane disruption in a number of different cells. Moreover, the ATP depletion-mediated change from apoptosis to necrosis is also associated with the increases of VAC. The increase in lysosomal size may due to intracellular self-digestion of dying cells. Big lysosomes are easy to rupture, and the release of hydrolytic enzymes from ruptured lysosomes can cause plasma membrane disruption.

Cell death during development

There are many ways to measure apoptosis and other forms of programmed cell death in development. Once nonmammalian embryos have passed the midblastula transition, or much earlier in mammalian embryos, apoptosis is similar to that seen in adult organisms, and is used to sculpt the animal, fuse bilateral tissues, and establish the structure of the nervous system and the immune system. Embryos present unique problems in that, in naturally occurring cell deaths, few cells are involved and they are frequently in very restricted regions. Thus, identification of apoptotic or other dying cells is more effectively achieved by microscopy-based techniques than by electrophoretic or cell-sorting techniques. Since embryos have many mitotic cells and are frequently more difficult to fix than adult tissues, it is best to confirm interpretations by the use of two or more independent techniques. Although natural embryonic deaths are frequently programmed and require protein synthesis, activation of a cell death pathway is often post-translational and assays for transcriptional or translational changes-as opposed to changes in aggregation of death-related molecules or proteolytic activation of enzymes-is likely to be uninformative. Also, embryos can frequently exploit partially redundant pathways, such that the phenotype of a knockout or upregulated death-related gene is often rather modest, even though the adult may develop response or regulation problems. For these reasons, the study of cell death in embryos is fascinating but researchers should be cautious in their analyses.

Programmed cell death in the neurulating embryo is prevented by the chaperone heat shock cognate 70

Neuronal cell death is a genuine developmental process, with precise regulation and defined roles. In striking contrast, characterization of cell death that occurs at early stages of neural development is very limited. We previously showed that embryonic proinsulin increases the level of the chaperone heat shock cognate 70 (Hsc70) and reduces the incidence of apoptosis in the neurulating chick embryo [de la Rosa, et al. (1998), Proc. Natl. Acad. Sci. USA, 95, 9950]. We now demonstrate that Hsc70 is directly involved in cell survival during neurulation, as specific downregulation of endogenous Hsc70 by antisense oligodeoxynucleotide interference provoked an increase in apoptosis both in vitro and in ovo. In parallel, activation of caspase-3 was increased after hsc70 antisense oligodeoxynucleotide treatment. Dead cells were located mostly in the developing nervous system, distributed in areas where the incidence of cell death was high. These areas coincided both in vivo and under different death-inducing conditions, including antisense interference and growth factor deprivation. Hsc70 immunostaining was strong in at least some areas of high cell death. Apoptotic cells within these areas presented undetectable Hsc70 levels, however, suggesting that this protein acts as an intrinsic protector of neuroepithelial and neural precursor cells.

Circulating nucleosomes in serum

In the nucleus of eukaryotic cells, DNA is associated with several protein components and forms complexes known as nucleosomes. During cell death, particularly during apoptosis, endonucleases are activated that cleave the chromatin into multiple oligo- and mononucleosomes. Subsequently, these nucleosomes are packed into apoptotic bodies and are engulfed by macrophages or neighboring cells. In cases of high rates of cellular turnover and cell death, they also are released into the circulation and can be detected in serum or plasma. As enhanced cell death occurs under various pathologic conditions, elevated amounts of circulating nucleosomes are not specific for any benign or malignant disorder. However, the course of change in the nucleosomal levels in circulation of patients with malignant tumors during chemotherapy or radiotherapy is associated with the clinical outcome and can be useful for the therapeutic monitoring and the prediction of the therapeutic efficacy.

Apoptotic versus autophagic cell death in heart failure

OBJECTIVE

Progressive loss of cardiomyocytes is one of the most important pathogenic characteristics of heart failure. Apoptosis may be an important mode of cell death in heart failure but it must be demonstrated by multiple criteria and not just TUNEL staining alone. Previously, we and others have demonstrated that besides apoptosis other phenomena like active gene transcription can result in TUNEL positivity. Moreover, other types of cell death that are caspase-independent could be important in heart failure. This study examined the hypothesis whether TUNEL labeling parallels caspase activation.

METHODS

Cardiac tissue of patients in the terminal stage of heart failure as a consequence of ischaemic cardiomyopathy (ICM) or dilated cardiomyopathy (DCM) were studied. Embryonic mice hearts were used for positive control for detection of the classical apoptosis.

RESULTS

In mice embryonic hearts we could clearly find apoptotic cell death detected by TUNEL labeling and immunohistochemistry for activated caspase-3. In heart failure, TUNEL-positive cardiomyocytes were negative for active caspase-3 but showed signs of active gene transcription (SC-35). However, autophagic cell death could be found in 0.3% of the cardiomyocytes. Autophagic cell death was demonstrated by granular cytoplasmic ubiquitin inclusions, an established marker of autophagocytosis in neurons. Interestingly, these autophagic cardiomyocytes were TUNEL and activated caspase-3 negative but were also negative for C9, a marker for necrosis. Western blot analysis confirmed that in cardiomyopathies no cleavage of caspase-3 and caspase-7 occurred.

CONCLUSION

The present study demonstrates two fundamentally different situations of cell death in cardiac tissue. In embryonic mice, cardiomyocytes undergo caspase-dependent cell death. However, cardiomyocytes in heart failure show caspase-independent autophagic cell death rather than apoptotic cell death.

Steroid-triggered death by autophagy

Programmed cell death is a critical part of normal development, removing obsolete tissues or cells and sculpting body parts to assume their appropriate form and function. Most programmed cell death occurs by apoptosis of individual cells or autophagy of groups of cells. Although these pathways have distinct morphological characteristics, they also have a number of features in common, suggesting some overlap in their regulation. A recent paper by Lee and Baehrecke provides further support for this proposal.(1) These authors present, for the first time, a genetic analysis of autophagy, using the steroid-triggered metamorphosis of Drosophila as a model system. They demonstrate a remarkable degree of overlap between the control of apoptosis and autophagy as well as a key role for the steroid-inducible gene E93 in directing the autophagic death response. This paper also shows that E93 can direct cell death independently from the known death-inducer genes, defining a novel death pathway in Drosophila.

The autophagosomal-lysosomal compartment in programmed cell death

In the last decade a tremendous progress has been achieved in understanding the control of apoptosis by survival and death factors as well as the molecular mechanisms of preparation and execution of the cell's suicide. However, accumulating evidence suggests that programmed cell death (PCD) is not confined to apoptosis but that cells use different pathways for active self-destruction as reflected by different morphology: condensation prominent, type I or apoptosis; autophagy prominent, type II; etc. Autophagic PCD appears to be a phylogenetically old phenomenon, it may occur in physiological and disease states. Recently, distinct biochemical and molecular features have been be assigned to this type of PCD. However, autophagic and apoptotic PCD should not be considered as mutually exclusive phenomena. Rather, they appear to reflect a high degree of flexibility in a cell's response to changes of environmental conditions, both physiological or pathological. Furthermore, recent data suggest that diverse or relatively unspecific signals such as photodamage or lysosomotropic agents may be mediated by lysosomal cysteine proteases (cathepsins) to caspases and thus, apoptosis. The present paper reviews morphological, functional and biochemical/molecular data suggesting the participation of the autophagosomal-lysosomal compartment in programmed cell death.

Nucleosomes in serum of patients with benign and malignant diseases

High quantities of mono- and oligonucleosomes circulate in the blood of patients with malignant tumors. For their direct quantification in serum, we modified the Cell Death Detection(plus)-ELISA for its application in liquid materials. We examined sera samples from 590 persons, including 418 patients with malignant tumors, 109 patients with benign diseases and 63 healthy persons. We also observed the kinetics of the concentration of nucleosomes in serum samples from 20 patients undergoing chemotherapy and from 16 patients undergoing radiotherapy. Sera of patients with malignant tumors contained considerably higher concentrations of nucleosomes (mean = 350 arbitrary units [AU], median = 190 AU) compared with those of healthy persons (mean = 36 AU, median = 24 AU; p = 0.0001) and patients with benign diseases (mean = 264 AU, median = 146 AU; p = 0.072). Concerning the follow-up investigations, the concentration of nucleosomes in serum increased 24-72 hr after the first application of chemotherapy and 6-24 hr after the start of radiotherapy. A subsequent decrease was often correlated with regression of the tumor. In patients undergoing chemotherapy, an increase in the baseline values of circulating nucleosomes >50%, which were determined before each new therapeutic cycle, was correlated with progression of disease; all patients with disease regression showed a decrease >50% of the baseline values. In patients undergoing radiotherapy, an early decrease of the nucleosomal concentration (< or = 1 day after the initial peak during therapy) to low minimum levels (< or = 100 AU) correlated with good clinical outcome; a late decrease (>1 day) to higher minimum levels (>100 AU) was associated with a worse clinical outcome. Thus, the concentration of nucleosomes in serum might be a useful tool for monitoring the biochemical response during antitumor therapy, especially for the early estimation of therapeutic efficacy.

Cytotoxicity tests for high-throughput drug discovery

Despite theoretical obstacles associated with performing cell-based assays in high-density formats (microplates with at least 384 wells), it is becoming clear that the pharmaceutical industry is now routinely running cell-based tests in these formats. This work is revealing the weakness of established cytotoxicity end points, specifically in relation to sensitivity and reproducibility. New assay kits based on bioluminescent detection of ATP and ADP are now providing the answer to these problems.

Cell death in the heart

The role of apoptosis in cardiac disease remains controversial. Much of the apoptosis detected, by chemical or molecular means, reflects inflammatory reaction and responding blood cells rather than myocytes, though their apoptosis in situ may exacerbate a bad situation, and their direct action against myocytes has not been excluded definitely. Myocyte apoptosis may reflect end-stage cardiac failure rather than causing it. If this is the case, then preventing apoptosis so that the cells can undergo necrosis does not accomplish much. Apoptosis is a consistent and important finding in many forms of cardiovascular disease. As determined by ultra-structure, apoptosis is common in cardiomyocytes, fibroblasts, vascular endothelial cells, and smooth muscle cells in cardiovascular disease of many origins. (62) Even though smooth muscle cells in atheromatous plaques appear to be necrotic,l it is likely that this is an evolved situation of apoptotic cells that were not removed. Given the prevalence of apoptotic processes in diseased heart and the very limited capacity of this organ to repair itself, (56) it is appropriate and justified to continue to explore the significance of apoptosis in cardiac disease and, above all, to explore the use of antiapoptotic agents in acute situations. Researchers must pay explicit attention to how they document cell death and in what tissues or cells it occurs. Otherwise, clinicians risk being deluded by preservation of morphology in nonfunctional cells and by confusion of what happened and where death occurred in the sequence of causality. Cell death in the heart is a matter of substantial theoretical and practical concern. A major problem in analyzing it is that, although apoptosis may be demonstrated easily in myocytes, particularly embryonic myocytes, under conditions of culture, interpretation is much more complex in an intact organ. The first issue is one of timing. In situations of severe, acute loss of cells, such as in an infarct, apoptotic cells may not be cleared rapidly and may progress to a more oncotic or necrotic morphology. Second, in situations of inflammation, biochemical or molecular techniques may confound apoptosis of inflammatory cells with apoptosis of myocytes. Third, priorities in the sequence of apoptosis differ between large, generally nonmitotic cells with massive cytoplasm (as differentiated myocytes) and small mitotic cells in culture, which usually are studied. The appearance and many markers of physiological cell death may differ from the most widely recognized forms of apoptosis, including late collapse of the nucleus and primacy of lysosomal or other proteases as opposed to caspases. Investigators should always strive to establish multiple criteria for apoptosis, with good documentation of timing and cell type. When these factors are taken into consideration, it seems that aggressive action against apoptosis may be of value in acute situations, such as infarct, in which buying short increments of time may reduce damage. In more chronic situations, much of the apoptosis detected derives from invading lymphocytes, mast cells, or other cells relating to inflammation. The apoptosis of these cells may exacerbate an already difficult situation, and intervention may prove of value. Otherwise, apoptosis of myocytes is more typically an end-stage situation, and it is more fruitful to alleviate the problem before this stage is reached.

Apoptosis-linked in vivo regulation of the tissue transglutaminase gene promoter

Tissue transglutaminase (tTG) is upregulated in various cells undergoing apoptosis. To investigate the transcriptional regulation of tTG a mouse strain carrying a beta-galactosidase reporter gene under the control of a 3.8 kilobase fragment of the tTG promoter was characterised. The transgene construct was shown to be expressed in the apoptotic regions of the mouse embryo. Here we report that the regulation of the transgene is also apoptosis-linked in adult animals. The transgene is induced in endocrine apoptosis involving mammary gland involution and corpus luteum regression. Induction of the reporter gene is detectable during in vivo but not in vitro apoptosis of thymocytes induced by the glucocorticoid receptor, the nur77, p53 and the retinoid receptor gamma mediated pathways. Additionally, the lacZ expression mimics the activation of the endogenous promoter in tissues characterised by high apoptotic turnover. These results suggest that the apoptosis-specific transcriptional regulation of tTG is mediated through elements of a 3.8 kb promoter and may require cosignals available only in tissue environment. Cell Death and Differentiation (2000) 7, 1225 - 1233.

Housekeeping genes commanded to commit suicide in CpG-cleavage commitment upstream of Bcl-2 inhibition in caspase-dependent and -independent pathways

A CpG-specific commitment common to both caspase-dependent and -independent cell deaths implies critical gene activity from epigenetic modulation. Using a focused microarray (genechip) of 22 housekeeping genes, which have canonical CpG islands at 5'-promoter regions, here we show critical regulation of vital intermediary metabolism and cell structure that are common to both caspase-dependent fasL-mediated and caspase-independent etoposide-mediated cell deaths. Gene activity of at least twofold under or over control levels and common to both cell death pathways was considered to be significantly regulated in common. Seven genes controlling energy production in glycolysis, tricarboxylic acid cycle, and the respiratory electron transport chain were significantly downregulated in common. Energy depletion is lethal. Downregulated pyruvate dehydrogenase E1 gene, in addition, suggested primary metabolic acidification. Cell acidification is also lethal. Critical derangement of the cell structure was suggested by common downregulation of the basal histone gene H2A.X which is required for nucleosome assembly. Common upregulation of the alpha-tubulin gene suggested perturbation of vital microtubular dynamics. Gene-commanded cell suicide was suggested. We further show that a Bcl-2 overexpression of three- to fourfold above normal levels could not prevent the CpG-specific megabase DNA cleavages in the two cell death pathways, but abolished their low-molecular-weight 200-bp ladder cleavages. Together with incomplete suppression of the other apoptotic expressions, the Bcl-2 inhibition point appeared downstream from the CpG-cleavage commitment point.