Differential involvement of DNases in HeLa cell apoptosis induced by etoposide and long term-culture

Human meibomian gland epithelial cell culture models: Current progress, challenges, and future directions

The widely used immortalised human meibomian gland epithelia cell (iHMGEC) line has made possible extensive studies of the biology and pathophysiology of meibomian glands (MG). Tissue culture protocols for iHMGEC have been revised and modified to optimise the growth conditions for cell differentiation and lipid accumulation. iHMGEC proliferate in serum-free medium but require serum or other appropriate exogenous factors to differentiate. Several supplements can enhance differentiation and neutral lipid accumulation in iHMGEC grown in serum-containing medium. In serum-free medium, rosiglitazone, a peroxisome proliferator activator receptor-γ (PPARγ) agonist, is reported to induce iHMGEC differentiation, neutral lipid accumulation and expression of key biomarkers of differentiation. iHMGEC cultured in serum-containing medium under hypoxia or with azithromycin increases DNAse 2 activity, a biomarker of terminal differentiation in sebocytes. The production of lipids with composition similar to meibum has not been observed in vitro and this remains a major challenge for iHMGEC culture. Innovative methodologies such as 3D ex vivo culture of MG and generation of MG organoids from stem cells are important for further developing a model that more closely mimics the in vivo biology of human MG and to facilitate the next generation of studies of MG disease and dry eye.

E3 Ubiquitin Ligase ASB17 Promotes Apoptosis by Ubiquitylating and Degrading BCLW and MCL1

Simple Summary

B-cell lymphoma-2 family proteins have been widely accepted as the critical regulators in cell apoptosis, often found to be abnormally expressed in many cancers. Among them, B-cell leukemia/lymphoma w and myeloid cell leukemia-1 are two pro-survival proteins. Here, we reported that the ankyrin repeat and SOCS box protein 17 can degrade the two proteins in a ubiquitylation -dependent way. Furthermore, we generated the first ASB17 knockout C57BL/6J mice line. The results revealed that ASB17 deficiency inhibited apoptosis but did not affect testes development. Moreover, the ASB17-deficient mice were more resistant to the stimuli of etoposide, Altogether, these findings indicate that ASB17 is a novel positive mediator of cell apoptosis.

Abstract

Apoptosis is a very important process of cell death controlled by multiple genes during which cells undergo certain events before dying. Apoptosis helps to clean the unnecessary cells and has critical physiological significance. Altered apoptosis results in a disorder of cell death and is associated with many diseases such as neurodegenerative diseases and cancers. Here, we reported that the ankyrin repeat and SOCS box protein 17 (ASB17) was mainly expressed in the testis and promoted apoptosis both in vivo and in vitro. Analyzing ASB17-deficient mice generated by using the CRISPR/Cas9 system, we demonstrated that ASB17 deficiency resulted in the reduction of apoptosis in spermatogenic cells, but it did not affect the development of spermatozoa or normal fertility. Next, in an in vivo model, ASB17 deficiency prevented the apoptosis of spermatogonia induced by etoposide in male mice. We noted that ASB17 promoted apoptosis in a caspase-dependent manner in vitro. Moreover, ASB17 interacted with the members of the BCL2 family, including BCL2, BCLX, BCLW, and MCL1. Interestingly, ASB17 specifically degraded the two anti-apoptotic factors, BCLW and MCL1, in a ubiquitylation-dependent fashion. Collectively, our findings suggested that ASB17 acted as a distinct positive regulator of cell apoptosis.

On the use of an appropriate TdT-mediated dUTP-biotin nick end labeling assay to identify apoptotic cells

Apoptosis is an essential cellular mechanism involved in many processes such as embryogenesis, metamorphosis, and tissue homeostasis. DNA fragmentation is one of the key markers of this form of cell death. DNA fragmentation is executed by endogenous endonucleases such as caspase-activated DNase (CAD) in caspase-dependent apoptosis. The TUNEL (TdT-mediated dUTP-biotin nick end labeling) technique is the most widely used method to identify apoptotic cells in a tissue or culture and to assess drug toxicity. It is based on the detection of 3'-OH termini that are labeled with dUTP by the terminal deoxynucleotidyl transferase. Although the test is very reliable and sensitive in caspase-dependent apoptosis, it is completely useless when cell death is mediated by pathways involving DNA degradation that generates 3'-P ends as in the LEI/L-DNase II pathway. Here, we propose a modification in the TUNEL protocol consisting of a dephosphorylation step prior to the TUNEL labeling. This allows the detection of both types of DNA breaks induced during apoptosis caspase-dependent and independent pathways, avoiding underestimating the cell death induced by the treatment of interest.

Multiple effects of the Na(+)/H (+) antiporter inhibitor HMA on cancer cells

Amiloride derivatives are a class of new promising chemotherapeutic agents. A representative member of this family is the sodium-hydrogen antiporter inhibitor HMA (5-(N,N-hexamethylene amiloride), which has been demonstrated to induce cellular intracytosolic acidification and cell death through the apoptotic pathway(s). This work aims at characterizing drug response of human cancer cell lines to HMA. After a first screening revealing that HMA interferes with cancer cell survival, we focused our attention on SW613-B3 colon carcinoma cells, which are intrinsically resistant to a panel of drugs. Searching for the activation of canonical apoptosis, we found that this process was abortive, given that the final steps of this process, i.e. PARP-1 cleavage and DNA ladder, were not detectable. Thus, we addressed caspase-independent paradigms of cell death and we observed that HMA promotes the induction of the LEI/L-DNase II pathway as well as of parthanatos. Finally, we explored the possible impact of autophagy of cell response to HMA, providing the evidence that autophagy is activated in our experimental system. On the whole, our results defined the biochemical reactions triggered by HMA, and elucidated its multiple effects, thus adding further complexity to the intricate network leading to drug resistance.

Multiple effects of berberine derivatives on colon cancer cells

The pharmacological use of the plant alkaloid berberine is based on its antibacterial and anti-inflammatory properties; recently, anticancer activity has been attributed to this compound. To exploit this interesting feature, we synthesized three berberine derivatives, namely, NAX012, NAX014, and NAX018, and we tested their effects on two human colon carcinoma cell lines, that is, HCT116 and SW613-B3, which are characterized by wt and mutated p53, respectively. We observed that cell proliferation is more affected by cell treatment with the derivatives than with the lead compound; moreover, the derivatives proved to induce cell cycle arrest and cell death through apoptosis, thus suggesting that they could be promising anticancer drugs. Finally, we detected typical signs of autophagy in cells treated with berberine derivatives.

Apoptosis-inducing factor (AIF) and leukocyte elastase inhibitor/L-DNase II (LEI/LDNaseII), can interact to conduct caspase-independent cell death

Programmed cell death is an important factor in tissue homeostasis. Lot of work has been performed to characterize the caspase-dependent cell death. Caspase-independent cell death, although important in many physiological situations, is less investigated. In this work we show that two caspase-independent effectors of cell death, namely apoptosis-inducing factor and leukocyte elastase inhibitor derived DNase II interact and can cooperate to induce cell death. These results contribute to the knowledge of molecular pathways of cell death, an important issue in the development of new therapeutic strategies for the treatment of cancer or neurodegenerative diseases.

RanBPM is an acetylcholinesterase-interacting protein that translocates into the nucleus during apoptosis

Acetylcholinesterase (AChE) expression may be induced during apoptosis in various cell types. Here, we used the C-terminal of AChE to screen the human fetal brain library and found that it interacted with Ran-binding protein in the microtubule-organizing center (RanBPM). This interaction was further confirmed by coimmunoprecipitation analysis. In HEK293T cells, RanBPM and AChE were heterogeneously expressed in the cisplatin-untreated cytoplasmic extracts and in the cisplatin-treated cytoplasmic or nuclear extracts. Our previous studies performed using morphologic methods have shown that AChE translocates from the cytoplasm to the nucleus during apoptosis. Taken together, these results suggest that RanBPM is an AChE-interacting protein that is translocated from the cytoplasm into the nucleus during apoptosis, similar to the translocation observed in case of AChE.

Changes of mitochondria and relocation of the apoptosis-inducing factor during apoptosis

During apoptosis, apoptosis-inducing factor (AIF) is released from the mitochondrial intermembrane space to the cytosol and to the nucleus. We analyzed AIF in HeLa cells driven to apoptosis by either etoposide or actinomycin D, and we observed changes in the structure and function of mitochondria as well as the translocation of cytochrome c and AIF from mitochondria to the nucleus in early apoptosis. In cells with fragmented chromatin (i.e., in late apoptosis), the immunolabeling for AIF appeared to be distinct from chromatin, being mainly confined to mitochondria.

Leukocyte elastase inhibitor: a new regulator of PARP-1

Poly(ADP-ribose) polymerase-1 (PARP-1) uses NAD(+) as a substrate to form ADP-ribose. During apoptosis, caspases cleave PARP-1 to avoid excessive NAD consumption. Because PARP-1 is a key regulator of the activity of DNases involved in caspase-dependent apoptosis, its cleavage is required to promote DNA degradation. To explore the situation in caspase-independent cell death, we investigated the effect of PARP-1 on the acid endonuclease leukocyte elastase inhibitor (LEI)-derived DNase II (L-DNase II). We found for the first time an association between PARP-1 and LEI/L-DNase II. Unexpectedly, we observed that LEI influenced the automodification of PARP-1.

Distribution of centromeric proteins and PARP-1 during mitosis and apoptosis

A large complex of proteins, called CENPs, are associated with centromeric DNA. Some of them exhibit a cell cycle-related expression (e.g., CENP-E and -F) and are required for the transition from interphase to mitosis, whereas constitutive proteins (e.g., CENP-A, -B, -C, -G, and -H) reside permanently at the centromere and are essential for the correct kinetochore assembly. Poly(ADP-ribose) polymerase-1 (PARP-1), which plays an active role in many basic processes, was described as a possible regulator of CENPs. By multicolor immunofluorescence we therefore analyzed the distribution of PARP-1 and its interaction with CENP-B, -E, and -F during mitosis and apoptosis.

Study of the effects of a new pyrazolecarboxamide: changes in mitochondria and induction of apoptosis

Drug resistance of cancer cells is often correlated with the evasion of apoptosis, thus a major goal in cancer research is to search for compounds able to counteract cancer by promoting apoptosis. A variety of compounds with anticancer activity are characterised by the presence of the pyrazole as core nucleus. We synthesised a panel of pyrrolyl-pyrazole-carboxamides and we focused on the new compound RS 2780 (N-2-phenylethyl 1-(4-chlorophenyl)-3-methyl-5-pyrrolylpyrazole-4-carboxamide). The biological effects of RS 2780 on cell proliferation and viability were first evaluated on human HeLa cancer cells. As revealed by cell growth and viability experiments, a 24-h treatment of HeLa cells with increasing concentrations of RS 2780 (ranging from 0.1 to 100 microM) proved to inhibit cell proliferation and to affect cell viability. Notably, the new compound was effective also on colon carcinoma SW613-B3 cells, which are extremely resistant to most drugs, while it does not alter the proliferation of normal fibroblasts. We observed that RS 2780 interferes with the structural and functional properties of mitochondria, leading to the activation of the mitochondria-dependent apoptotic pathway. Apoptosis occurrence was supported by a number of morphological and biochemical hallmarks, including chromatin condensation, internucleosomal DNA fragmentation, PARP-1 cleavage and caspase activation. In conclusion, our results demonstrate for the first time the antiproliferative properties of the new compound RS 2780 on HeLa and SW613-B3 cancer cells and show that its effects on mitochondria lead to apoptosis.

Regulation of poly(ADP-ribose) polymerase-1 functions by leukocyte elastase inhibitor/LEI-derived DNase II during caspase-independent apoptosis

Poly(ADP-ribose) polymerase-1 (PARP-1) is an important regulator of apoptosis. Its over-activation at the onset of apoptosis can inhibit the action of apoptotic endonucleases like caspase-activated DNase and DNAS1L3. Therefore, controlled PARP-1 proteolysis during caspase-dependent apoptosis is considered essential to promote DNA degradation. Yet, little is known about the interplay of PARP-1 and endonucleases that operate during caspase-independent cell death. Here we show that in the long-term cultured HeLa cells which undergo caspase-independent death, PARP-1 co-immunoprecipitates with leukocyte elastase inhibitor-derived DNase II (L-DNase II), an acid DNase implicated in this death pathway and activated by serine proteases. Our results indicate that, despite having putative poly(ADP-ribose)-acceptor sites, LEI/L-DNase II is neither significantly poly(ADP-ribosyl)ated nor inhibited by PARP-1 during caspase-independent apoptosis. Unexpectedly, caspase-independent apoptosis induced by hexa-methylene amiloride, LEI/L-DNase II can activate PARP-1 and promote its auto-poly(ADP-ribosyl)ation, thus inhibiting PARP-1 activity. Moreover, overexpression of LEI blocks the pro-survival effect of PARP-1 in this model of cell death. Our results provide the original evidence for a new mechanism of PARP-1 activity regulation in the caspase-independent death pathway involving LEI/L-DNase II.

Nuclear export of LEI/L-DNase II by Crm1 is essential for cell survival

LEI/L-DNase II is the key protein of a caspase-independent pathway activated by serine proteases. LEI (Leukocyte elastase inhibitor), L-DNase II precursor, is a member of the clade B serpins (also called serpin b1). In its native conformation it inhibits several intracellular proteases and has an anti-apoptotic activity. Following a metabolic stress and the increase of protease activity in the cell, LEI is cleaved and transformed into L-DNase II (LEI-derived DNase II). This transformation is due to a conformational modification that exposes a nuclear localization signal and an endonuclease active site. In this paper we show that LEI can bind the exportin Crm1, and we identify on LEI a nuclear export signal involved in the control of LEI/L-DNase II nuclearization in healthy cells. Point mutation of this site increases the accumulation of the molecule in the nucleus and triggers cell death.

Conformational modification of serpins transforms leukocyte elastase inhibitor into an endonuclease involved in apoptosis

The best-characterized biochemical feature of apoptosis is degradation of genomic DNA into oligonucleosomes. The endonuclease responsible for DNA degradation in caspase-dependent apoptosis is caspase-activated DNase. In caspase-independent apoptosis, different endonucleases may be activated according to the cell line and the original insult. Among the known effectors of caspase-independent cell death, L-DNase II (LEI [leukocyte elastase inhibitor]-derived DNase II) has been previously characterized by our laboratory. We have thus shown that this endonuclease derives from the serpin superfamily member LEI by posttranslational modification (A. Torriglia, P. Perani, J. Y. Brossas, E. Chaudun, J. Treton, Y. Courtois, and M. F. Counis, Mol. Cell. Biol. 18:3612-3619, 1998). In this work, we assessed the molecular mechanism involved in the change in the enzymatic activity of this molecule from an antiprotease to an endonuclease. We report that the cleavage of LEI by elastase at its reactive center loop abolishes its antiprotease activity and leads to a conformational modification that exposes an endonuclease active site and a nuclear localization signal. This represents a novel molecular mechanism for a complete functional conversion induced by changing the conformation of a serpin. We also show that this molecular transformation affects cellular fate and that both endonuclease activity and nuclear translocation of L-DNase II are needed to induce cell death.

Proapoptotic effect of Uncaria tomentosa extracts

Uncaria tomentosa ("Uña de gato") (Rubiaceae) is widely used in South America for treatment of gastritis, arthritis, cancer and inflammatory conditions. Recent literature reports cytostatic, antiproliferative, anti-inflammatory, mutagenic and anti-mutagenic properties of extracts of the plant. The present study investigates the possible proapoptotic mechanism via the activation of caspase3, in cytostatic effects of root bark extracts of Uncaria tomentosa on three different tumoral cell lines.

Acid DNases and their interest among apoptotic endonucleases

Apoptosis is characterized by cell shrinkage, nuclear condensation and internucleosomal DNA cleavage. Besides the central role of caspases and other proteases, cell death triggers DNA degradation so that DNases have an active role in apoptotic cell death. The best-characterized apoptotic DNase is CAD, a neutral Mg-dependent endonuclease. Its activity is regulated by its inhibitor, ICAD, which is cleaved by caspases. Other neutral DNases have been shown to cleave nuclear DNA in apoptotic conditions: endonuclease G, GADD. In cells, the cytosolic pH is maintained to 7.2, mostly due to the activity of the Na(+)/H(+) exchanger. In many apoptotic conditions, a decrease of the intracellular pH has been shown. This decrease may activate different acid DNases, mostly when pH decreases below 6.5. Three acidic DNases II are so far known: DNase II alpha, DNase II beta and L-DNase II, a DNase II, derived from the serpin LEI (Leukocyte Elastase Inhibitor). Their activation during cell death is discussed in this review.

Irreversible pan-ErbB tyrosine kinase inhibitor CI-1033 induces caspase-independent apoptosis in colorectal cancer DiFi cell line

The epidermal growth factor receptor (EGFR) is overexpressed in the majority of colorectal carcinomas and represents a target for therapeutic interventions with signal transduction inhibitors. We investigated the ability of CI-1033 to induce apoptosis and inhibition of proliferation in the colorectal cancer cell lines DiFi and Caco-2, which both express high levels of EGFR. While in Caco-2 cells CI-1033 treatment at a concentration 0.1 microM for 72 hours demonstrated only antiproliferative (53.7 +/- 4.3%) but no pro-apoptotic effects, treatment of DiFi cells resulted in a reduced proliferation rate (31.4 +/- 3.1%) and in apoptosis (44.2 +/- 8.9%). In order to define proteins involved in the regulation of apoptosis, we aimed to determine differences in the proteome profile of both cell lines before and after treatment with CI-1033. Cellular proteins were analyzed by 2-D gel electrophoresis followed by computational image analysis and mass spectrometry. Our data show that DiFi cells differ from Caco-2 cells in nine significantly upregulated proteins, and their potential role in apoptosis is described. We demonstrate that induction of apoptosis was triggered via caspase-independent pathways. Overexpression of leukocyte elastase inhibitor (LEI) and translocation of cathepsin D to the cytosol accompanied by upregulation of other defined proteins resulted in Bax-independent AIF translocation from mitochondria into the nucleus and apoptosis. Definition of these proteins can pave the way for functional studies and contribute to a better understanding of the effects of CI-1033 and the pathways of caspase-independent cell death.

Trashing the genome: the role of nucleases during apoptosis

Two classes of nucleases degrade the cellular DNA during apoptosis. Cell-autonomous nucleases cleave DNA within the dying cell. They are not essential for apoptotic cell death or the life of the organism, but they might affect the efficiency of the process. By contrast, waste-management nucleases are essential for the life of the organism. In post-engulfment DNA degradation, the DNA of apoptotic cells is destroyed in lysosomes of the cells that have phagocytosed the corpses. Waste-management nucleases also destroy DNA that is released into the extracellular compartment. Here, we describe the complex group of nucleases that are involved in DNA destruction during apoptotic cell death.

The LEI/L-DNase II pathway is activated in light-induced retinal degeneration in rats

Retinal death induced by light seems to be a caspase-independent process. In this work we investigate the LEI/L-DNase II pathway, a caspase-independent pathway, in light-induced retinal degeneration in Fischer rats. Measurement of DNase activity in total retinal extracts of light exposed Fischer rats was performed by analysing a plasmid degradation on an agarose gel. The same method was used to measure the in vitro activity of recombinant LEI (reticulocyte lysate) after incubation with calpains. L-DNase II activity is observed in retinal extracts of light exposed Fischer rats and increases with time illumination. In this apoptotic death, the activation of calpains has been shown. Here we show that L-DNase II activation is not catalized by calpains. The present study indicates that the LEI/L-DNase II may be a possible pathway activated during photoreceptor apoptosis in light-induced retinal degeneration but that this pathway is not directly activated by calpains.

An antagonist of retinoic acid receptors more effectively inhibits growth of human prostate cancer cells than normal prostate epithelium

Screening of synthetic retinoids for activity against prostate carcinoma cell lines has identified antagonists of retinoic acid receptors (RARs) as potent growth inhibitors (Hammond et al, 2001, Br J Cancer 85, 453–462). Here we report that 5 days of exposure to a high-affinity pan-RAR antagonist (AGN194310) abolished growth of prostate carcinoma cells from 14 out of 14 patients, with half-maximal inhibition between 200 and 800 nM. It had similar effects (at ∼250 nM) on the prostate carcinoma lines LNCaP, DU-145 and PC-3. AGN194310 inhibited the growth of normal prostate epithelium cells less potently, by 50% at ∼1 μM. The growth of tumour cells was also inhibited more than that of normal cells when RARβ together with RARγ, but not RARα alone, were antagonised. Treatment of LNCaP cells with AGN194310 arrested them in G1 of cell cycle within 12 h, with an accompanying rise in the level of p21^waf1. The cells underwent apoptosis within 3 days, as indicated by mitochondrial depolarisation, Annexin V binding and DNA fragmentation. Apoptosis was caspase-independent: caspases were neither cleaved nor activated, and DNA fragmentation was unaffected by the pan-caspase inhibitor Z-VAD-FMK. The ability of AGN 194310 to induce apoptosis of prostate cancer cells and its differential effect on malignant and normal prostate epithelial cells suggests that this compound may be useful in the treatment of prostate cancer.

Cornea Graft Endothelial Cells Undergo Apoptosis by Way of an Alternate (Caspase-Independent) Pathway

PURPOSE

To look for apoptosis pathways involved in corneal endothelial cell death during acute graft rejection and to evaluate the potential role of nitric oxide in this process.

MATERIALS AND METHODS

Corneal buttons from Brown-Norway rats were transplanted into Lewis rat corneas. At different time intervals after transplantation, apoptosis was assessed by diamino-2-phenylindol staining and annexin-V binding on flat-mount corneas, and by terminal transferase dUTP nick end labeling (TUNEL), caspase-3 dependent and leukocyte elastase inhibitor (LEI)/LDNase II caspase-independent pathways on sections. Inducible nitric oxide synthase (NOS-II) expression and the presence of nitrotyrosine were assayed by immunohistochemistry.

RESULTS

Graft endothelial cells demonstrated nuclear fragmentation and LEI nuclear translocation, annexin-V binding, and membranes bleb formation. Apoptosis associated with caspase-3 activity or TUNEL-positive reaction was not observed at any time either in the graft or in the recipient corneal endothelial cells. During 14 days posttransplantation, the recipient corneal endothelial cells remained unaltered and their number unchanged in all studied corneas. NOS-II was expressed in infiltrating cells present within the graft. This expression was closely associated with the presence of nitrotyrosine in endothelial and infiltrating cells.

CONCLUSION

During the time course of corneal graft rejection, graft endothelial cells undergo apoptosis. Apoptosis is caspase 3 independent and TUNEL negative and is, probably, carried out by an alternative pathway driven by an LEI/L-Dnase II. Peroxynitrite formation may be an additional mechanism for cell toxicity and programmed cell death of the graft endothelial cells during the rejection process in this model.

Programmed cell deaths. Apoptosis and alternative deathstyles

Programmed cell death is a major component of both normal development and disease. The roles of cell death during either embryogenesis or pathogenesis, the signals that modulate this event, and the mechanisms of cell demise are the major subjects that drive research in this field. Increasing evidence obtained both in vitro and in vivo supports the hypothesis that a variety of cell death programs may be triggered in distinct circumstances. Contrary to the view that caspase-mediated apoptosis represents the standard programmed cell death, recent studies indicate that an apoptotic morphology can be produced independent of caspases, that autophagic execution pathways of cell death may be engaged without either the involvement of caspases or morphological signs of apoptosis, and that even the necrotic morphology of cell death may be consistently produced in some cases, including certain plants. Alternative cell death programs may imply novel therapeutic targets, with important consequences for attempts to treat diseases associated with disregulated programmed cell death.

Apoptosis induced by Na+/H+ antiport inhibition activates the LEI/L-DNase II pathway

L-DNase II is derived from its precursor leucocyte elastase inhibitor (LEI) by post-translational modification. In vitro, the conversion of LEI into L-DNase II can be induced by incubation of LEI at an acidic pH. In this study, we proposed to analyze the effects of intracellular acidification on this transformation. Amiloride derivatives, like hexamethylene amiloride (HMA), are known to provoke a decrease of cytosolic pH by inhibiting the Na(+)/H(+) antiport. In BHK cells, treatment with HMA-induced apoptosis accompanied by an increase in L-DNase II immunoreactivity and L-DNase II enzymatic activity. Overexpression of L-DNase II precursor led to a significant increase of apoptosis in these cells supporting the involvement of L-DNase II in HMA induced apoptosis. As previously shown in other cells, etoposide-induced apoptosis did not activate L-DNase. On the contrary, LEI overexpression significantly increased cell survival in etoposide-induced apoptosis. Together these results suggest differential roles of LEI and L-DNase II in response to different types of apoptotic inducers.

Retinoic acid inhibits elastase-induced injury in human lung epithelial cell lines

The protective effects of retinoic acid on elastase-induced lung epithelial cell injury were studied using elastase extracted from purulent human sputum, the BEAS-2B human bronchial epithelial cell line, A549 human type II lung cell line, and primary cultures of human tracheal epithelial cells. Elastase decreased viability of BEAS-2B cells, A549 cells, and human tracheal epithelial cells in concentration- and time-dependent fashions. Elastase also induced apoptosis of BEAS-2B cells, A549 cells, and the tracheal epithelial cells detected with cell death detection enzyme-linked immunosorbent assay and terminal deoxyribonucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) methods. Retinoic acid alone did not affect the viability of BEAS-2B cells, A549 cells, or the tracheal epithelial cells, and did not induce apoptosis of the cells. However, retinoic acid prevented the decreases in the viability and reduced apoptosis of BEAS-2B cells, A549 cells, and the tracheal epithelial cells induced by elastase. Likewise, retinoic acid inhibited caspase 3 activity in BEAS-2B cells and A549 cells induced by elastase, as well as proteolytic activity of elastase. Furthermore, caspase 3 inhibitor inhibited the elastase-induced apoptosis of the cells. These findings suggest that retinoic acid may inhibit elastase-induced lung epithelial cell injury partly through the inhibition of proteolytic activity of elastase and through the inhibition of caspase 3 activity by elastase. Retinoic acid may, therefore, have protective effects against the elastase-induced lung injury and subsequent development of pulmonary emphysema.

Induction of acetylcholinesterase expression during apoptosis in various cell types

Acetylcholinesterase (AChE) plays a key role in terminating neurotransmission at cholinergic synapses. AChE is also found in tissues devoid of cholinergic responses, indicating potential functions beyond neurotransmission. It has been suggested that AChE may participate in development, differentiation, and pathogenic processes such as Alzheimer's disease and tumorigenesis. We examined AChE expression in a number of cell lines upon induction of apoptosis by various stimuli. AChE is induced in all apoptotic cells examined as determined by cytochemical staining, immunological analysis, affinity chromatography purification, and molecular cloning. The AChE protein was found in the cytoplasm at the initiation of apoptosis and then in the nucleus or apoptotic bodies upon commitment to cell death. Sequence analysis revealed that AChE expressed in apoptotic cells is identical to the synapse type AChE. Pharmacological inhibitors of AChE prevented apoptosis. Furthermore, blocking the expression of AChE with antisense inhibited apoptosis. Therefore, our studies demonstrate that AChE is potentially a marker and a regulator of apoptosis.

Nuclear apoptosis detection by flow cytometry: influence of endogenous endonucleases

Nuclear apoptosis is characterized by chromatin condensation and progressive DNA cleavage into high-molecular-weight fragments and oligonucleosomes. These complex phenomena can be mediated by the activation of a multiplicity of enzymes, characterized by specific patterns of cation dependance, pH requirement, and mode of activation. The significance of this multiplicity of enzymes that cleave genomic DNA has been attributed to the need of death effector pathways specific for cell types/tissues, the level of cell differenciation, and the nature of the apoptotic stimuli. The activation of these factors contributes to the development of alterations that can be detected specifically by flow cytometric assays, namely, propidium iodide assays, acridine orange/ethidium bromide double staining, the TUNEL and ISNT techniques, and the assays of DNA sensitivity to denaturation. Although applicable to a wide spectrum of cell types, an increasing body of literature indicates that these techniques cannot be universally applied to all cell lines and apoptotic conditions: The requirement of a particular mediator(s) of nuclear apoptosis or the absence of endonuclease activity can limit the relevance of certain techniques. Finally, endonucleases recruited during primary necrosis can introduce nuclear alterations detected by some assays and raise the problem of their specificity. This review underlines the need for strategies to accurately detect and quantify nuclear apoptosis by flow cytometry when new cell systems and apoptotic conditions are considered.

Increased expression of intranuclear AChE involved in apoptosis of SK-N-SH cells

Programmed cell death plays an integral role in neurodegenerative diseases such as Alzheimer's disease (AD). Acetylcholinesterase (AChE) was suggested to be neurotoxic in vivo and in vitro and accelerate assembly of amyloid peptide into Alzheimer's fibrils. In our experiments, we found increased AChE expression in apoptotic neuroblastoma SK-N-SH cells after long-term culture. Our results first showed that in apoptotic SK-N-SH cells, AChE aggregated in the nucleus and suppression of AChE expression with antisense oligonucleotide could save the cells from apoptosis. It was also found that caspase-3 activity was parallel with AChE activation in apoptotic SK-N-SH cells. These results suggest that AChE plays an important role in the procession of neuroblastoma cell apoptosis and favor the association between AChE and neuronal apoptosis in AD.

Poly(ADP-ribose) polymerase cleavage during apoptosis: when and where?

Poly(ADP-ribose) polymerase-1 (PARP-1) plays the active role of "nick sensor" during DNA repair and apoptosis, when it synthesizes ADP-ribose from NAD(+) in the presence of DNA strand breaks. Moreover, PARP-1 becomes a target of apoptotic caspases, which originate two proteolytic fragments of 89 and 24 kDa. The precise relationship between PARP-1 activation and degradation during apoptosis is still a matter of debate. In human Hep-2 cells driven to apoptosis by actinomycin D, we have monitored PARP-1 activity by the mAb 10H, which is specific for the ADP-ribose polymers, and we have observed that poly(ADP-ribose) synthesis is a very early response to the apoptotic stimulus. The analysis of the presence and fate of the p89 proteolytic fragment revealed that PARP-1 proteolysis by caspases is concomitant with poly(ADP-ribose) synthesis and that p89 migrates from the nucleus into the cytoplasm in late apoptotic cells with advanced nuclear fragmentation.

Elastase is not required for L-DNase II activation during apoptosis in developing chicken neural retina

During retinal development, the neuronal death is carried out by the mechanism of apoptosis. Among the different endonucleases activated, L-DNase II seems to be responsible for most of DNA degradation in this tissue. L-DNase II derives from LEI (Leukocyte Elastase Inhibitor) by a post-translational modification carried out by elastase in apoptosis induced in vitro. In this study, we investigated whether elastase could be implicated in apoptosis occurring during retinal development. Although elastase and LEI/elastase complex are colocalized in retinal sections, the LEI/elastase complex, detected by Western blot, does not change at all stages of development. However, at pH 4 retinal extracts show an enhanced activation of the L-DNase II. These results suggest that an acid protease, such as a cathepsin, may be implicated in neuronal retinal apoptosis.

Involvement of L-DNase II in nuclear degeneration during chick retina development

During the development of the neural retina, 50% of the neurons die physiologically by apoptosis. In the chick embryo, the apoptotic wave starts at E8 and ends at E18, with a peak at E11. The onset of apoptosis is accompanied by the activation of several degradative enzymes. Among these, the activation of the endonucleases leads to the degradation of the genomic DNA of the cell which is thought to be the final event in apoptosis. Here, we have investigated the endonucleases activated during apoptosis associated with retinal development. We have found that Ca2+-Mg2+-dependent endonucleases, as well as acid endonucleases are activated. The results obtained in vitro using purified nuclei from chicken retina indicate that the endonuclease activity resulting from the activation of L-DNase II, an acid DNase is responsible for most of the DNA degradation observed in these cells.

A caspase-independent cell clearance program. The LEI/L-DNase II pathway

The discovery of caspase-mitochondrial pathway counts as one of the most important discovery in apoptosis biochemistry. Today, however, we begin to recognize its limits. Inhibition of caspase does not prevent cell death in many mammalian models. Targeted disruption of caspases does not impair every type of apoptosis. Other pathways, caspase independent, are now described. Here we present one of these pathways. It is a serine-protease dependent pathway and its key event is the transformation of LEI (a serine protease inhibitor) into L-DNase II (an endonuclease). When using this apoptotic pathway the cell activates, at the same time, its endonuclease activity (L-DNase II appears) and its protease activity (there is a release of inhibition of proteases).

Characterization of two DNase gamma-specific monoclonal antibodies and the in situ detection of DNase gamma in the nuclei of apoptotic rat thymocytes

Two novel monoclonal antibodies (mAbs), hg302 and hg303, raised against a synthetic peptide corresponding to the basic domain of human DNase gamma, are characterized in detail. In Western blot analysis, hg303 recognizes both wild type and C-terminal Myc-His-tagged human DNase gamma, but does not cross-react with human DNase I family members, DNase I, DNase X, or DNAS1L2. On the other hand, dot blot analysis reveals the fine specificity of hg302; it recognizes human, mouse, and rat DNase gamma, but not other DNase I family DNases under non-denaturing conditions. Furthermore, hg302 efficiently immunoprecipitates wild type, but not C-terminal Myc-His-tagged, human DNase gamma from cell lysates. In immunohistochemical analysis, hg302 strongly recognizes DNase gamma in the nuclei of X-ray irradiation-induced apoptotic, but not normal rat thymocytes. The specific detection of DNase gamma in apoptotic nuclei is confirmed by indirect-immunofluorescence analysis using TNF-alpha-induced apoptotic HeLa S3 cells transfected with DNase gamma. These results, together with the observations that DNase gamma is present in normal thymocytes and its activity is unchanged during the apoptosis, suggest that some molecular change(s), which triggers the activation of DNase gamma, occurs in response to apoptotic stimuli in the basic domain, and hg302 specifically recognizes the activated DNase gamma in immunohistochemical analysis.

DNases and apoptosis

Here we review the different apoptotic DNases. From a functional point of view, DNases implicated in apoptosis may be classified into three groups: the Ca2+/Mg2+endonucleases, the Mg2+-endonucleases, and the cation-independent endonucleases. The first group includes DNase I which has no specificity for the linker region, DNase gamma which has some homology with DNase I, and other DNases which cleave DNA in the linker region. Both DNase I and DNase gamma have been cloned. The other nucleases of this category have dispersed molecular weights. Their sequences are unknown and it is difficult to determine their role(s) in apoptosis. It seems that different pathways are present and that these nucleases may be activated either by caspases or serine proteases. The caspase 3 activated DNase (CAD, CPAN, or DFF40) belongs to the Mg2+-dependent endonucleases. DNase II belongs to the third group of acid endonucleases or cation-independent DNases. We have shown the involvement of DNase II in lens cell differentiation. Recently, the molecular structure of two different enzymes has been elucidated, one of which has a signal peptide and appears to be secreted. The other, called L-DNase II, is an intracellular protein having two enzymatic activities; in its native form, it is an anti-protease, and after posttranslational modification, it becomes a nuclease.Key words: endonucleases, apoptosis, caspases, serine proteases.

Sequence of lethal events in HeLa cells exposed to the G2 blocking cytolethal distending toxin

The bacterial cytolethal distending toxin (CDT) was previously shown to block the cell cycle of several cell lines at stage G2 through inactivation of the cyclin-dependent kinase Cdkl and without induction of DNA strand breaks. In the present study, we have analyzed, using various methods of analytical cytometry, the progressive transformation and delayed lethal events in the tumor-derived HeLa cell line temporarily exposed to CDT. The cell proliferation arrest induced by CDT was irreversible but, starting about two days after exposure, the G2 block released partially, concomitantly with a decline in the level of Cdkl phosphorylation. This partial release resulted in endoreduplication, leading to the emergence of a significant subpopulation of cells with a 8C DNA content, and by multipolar abortive mitosis which accounted for the mortality recorded 2 and 3 days after exposure. The other major lethal event was a micronucleation process which started to be significant about 3 days after exposure and amplified later on. Both multipolar abortive mitosis and micronucleation appeared topologically related to centrosomal amplification.