All along the watchtower: on the regulation of apoptosis regulators

The Regulatory Roles of Mitochondrial Calcium and the Mitochondrial Calcium Uniporter in Tumor Cells

Mitochondria, as the main site of cellular energy metabolism and the generation of oxygen free radicals, are the key switch for mitochondria-mediated endogenous apoptosis. Ca²⁺ is not only an important messenger for cell proliferation, but it is also an indispensable signal for cell death. Ca²⁺ participates in and plays a crucial role in the energy metabolism, physiology, and pathology of mitochondria. Mitochondria control the uptake and release of Ca²⁺ through channels/transporters, such as the mitochondrial calcium uniporter (MCU), and influence the concentration of Ca²⁺ in both mitochondria and cytoplasm, thereby regulating cellular Ca²⁺ homeostasis. Mitochondrial Ca²⁺ transport-related processes are involved in important biological processes of tumor cells including proliferation, metabolism, and apoptosis. In particular, MCU and its regulatory proteins represent a new era in the study of MCU-mediated mitochondrial Ca²⁺ homeostasis in tumors. Through an in-depth analysis of the close correlation between mitochondrial Ca²⁺ and energy metabolism, autophagy, and apoptosis of tumor cells, we can provide a valuable reference for further understanding of how mitochondrial Ca²⁺ regulation helps diagnosis and therapy.

Next-Generation Sequencing Reveals Differential Responses to Acute versus Long-Term Exposures to Graphene Oxide in Human Lung Cells

Numerous studies have addressed the biological impact of graphene-based materials including graphene oxide (GO), yet few have focused on long-term effects. Here, RNA sequencing is utilized to unearth responses of human lung cells to GO. To this end, the BEAS-2B cell line derived from normal human bronchial epithelium is subjected to repeated, low-dose exposures of GO (1 or 5 µg mL^-1 ) for 28 days or to the equivalent, cumulative amount of GO for 48 h. Then, samples are analyzed by using the NovaSeq 6000 sequencing system followed by pathway analysis and gene ontology enrichment analysis of the differentially expressed genes. Significant differences are seen between the low-dose, long-term exposures and the high-dose, short-term exposures. Hence, exposure to GO for 48 h results in mitochondrial dysfunction. In contrast, exposure to GO for 28 days is characterized by engagement of apoptosis pathways with downregulation of genes belonging to the inhibitor of apoptosis protein (IAP) family. Validation experiments confirm that long-term exposure to GO affects the apoptosis threshold in lung cells, accompanied by a loss of IAPs. These studies reveal the sensitivity of RNA-sequencing approaches and show that acute exposure to GO is not a good predictor of the long-term effects of GO.

Apoptosis, Chemoresistance, and Breast Cancer: Insights From the MCF-7 Cell Model System

The MCF-7 cell line was derived from a patient with metastatic breast cancer in 1970. Since then it has become a prominent model system for the study of estrogen receptor-positive breast cancer. With this model as a focus, this review summarizes important studies addressing tumor necrosis factor-α as a prototypical apoptosis-inducing cytokine in MCF-7 cells. Both survival and death receptor signaling pathways are discussed in terms of their role in chemotherapy-induced apoptosis as well as in chemoresistance. Novel therapeutic approaches to the treatment of breast cancer are proposed utilizing knowledge of these signaling pathways as targets. Specifically, ceramide metabolism is proposed as a novel target for chemosensitivity, perhaps combined with selective inhibitors of Bcl-2 or PI3K/Akt/nuclear factor-κB. Suggested areas of future research include translational studies manipulating candidate survival and death signaling pathways.

Identifying Novel Candidate Genes Related to Apoptosis from a Protein-Protein Interaction Network

Apoptosis is the process of programmed cell death (PCD) that occurs in multicellular organisms. This process of normal cell death is required to maintain the balance of homeostasis. In addition, some diseases, such as obesity, cancer, and neurodegenerative diseases, can be cured through apoptosis, which produces few side effects. An effective comprehension of the mechanisms underlying apoptosis will be helpful to prevent and treat some diseases. The identification of genes related to apoptosis is essential to uncover its underlying mechanisms. In this study, a computational method was proposed to identify novel candidate genes related to apoptosis. First, protein-protein interaction information was used to construct a weighted graph. Second, a shortest path algorithm was applied to the graph to search for new candidate genes. Finally, the obtained genes were filtered by a permutation test. As a result, 26 genes were obtained, and we discuss their likelihood of being novel apoptosis-related genes by collecting evidence from published literature.

Methyl protodioscin induces G2/M cell cycle arrest and apoptosis in A549 human lung cancer cells

Background:

Methyl protodioscin (MPD) is a furostanol bisglycoside with antitumor properties. It has been shown to reduce proliferation, cause cell cycle arrest.

Objective:

The present study elucidates the mechanism underlying MPD's apoptotic effects, using the A549 human lung cancer cell line.

Materials and Methods:

The human pulmonary adenocarcinoma cell line A549 was obtained from the Cell Bank of the Animal Experiment Center, North School Region, Sun Yat-Sen University. All of the cells were grown in RPMI 1640 supplemented with 10% fetal calf serum (Hyclone, Logan, UT, USA), penicillin (10,000 U/l), and streptomycin (100 mg/l) at 37°C in a 5% CO₂ humidified atmosphere. The induction of apoptosis was observed in flow cytometry and fluorescent staining experiments.

Results:

MPD showed growth inhibitory effects in A549 cells in a dose- and time-dependent manner. The significant G2/M cell cycle arrest and apoptotic effect were also seen in A549 cells treated with MPD. MPD-induced apoptosis was accompanied by a significant reduction of mitochondrial membrane potential, release of mitochondrial cytochrome c to cytosol, activation of caspase-3, downregulation of Bcl-2, p-Bad, and upregulation of Bax.

Conclusion:

Our results show that the induction of apoptosis by MPD involves multiple molecular pathways and strongly suggest that Bcl-2 family proteins signaling pathways. In addition, mitochondrial membrane potential, mitochondrial cytochrome c and caspase-3 were also closely associated with MPD-induced apoptotic process in human A549 cells.

Biological responses of three-dimensional cultured fibroblasts by sustained compressive loading include apoptosis and survival activity

Pressure ulcers are characterized by chronicity, which results in delayed wound healing due to pressure. Early intervention for preventing delayed healing due to pressure requires a prediction method. However, no study has reported the prediction of delayed healing due to pressure. Therefore, this study focused on biological response-based molecular markers for the establishment of an assessment technology to predict delayed healing due to pressure. We tested the hypothesis that sustained compressive loading applied to three dimensional cultured fibroblasts leads to upregulation of heat shock proteins (HSPs), CD44, hyaluronan synthase 2 (HAS2), and cyclooxygenase 2 (COX2) along with apoptosis via disruption of adhesion. First, sustained compressive loading was applied to fibroblast-seeded collagen sponges. Following this, collagen sponge samples and culture supernatants were collected for apoptosis and proliferation assays, gene expression analysis, immunocytochemistry, and quantification of secreted substances induced by upregulation of mRNA and protein level. Compared to the control, the compressed samples demonstrated that apoptosis was induced in a time- and load- dependent manner; vinculin and stress fiber were scarce; HSP90α, CD44, HAS2, and COX2 expression was upregulated; and the concentrations of HSP90α, hyaluronan (HA), and prostaglandin E₂ (PGE₂) were increased. In addition, the gene expression of antiapoptotic Bcl2 was significantly increased in the compressed samples compared to the control. These results suggest that compressive loading induces not only apoptosis but also survival activity. These observations support that HSP90α, HA, and, PGE₂ could be potential molecular markers for prediction of delayed wound healing due to pressure.

Evaluation of the BH3-only protein Puma as a direct Bak activator

Interactions among Bcl-2 family proteins play critical roles in cellular life and death decisions. Previous studies have established the BH3-only proteins Bim, tBid, and Noxa as "direct activators" that are able to directly initiate the oligomerization and activation of Bak and/or Bax. Earlier studies of Puma have yielded equivocal results, with some concluding that it also acts as a direct activator and other studies suggesting that it acts solely as a sensitizer BH3-only protein. In the present study we examined the interaction of Puma BH3 domain or full-length protein with Bak by surface plasmon resonance, assessed Bak oligomerization status by cross-linking followed by immunoblotting, evaluated the ability of the Puma BH3 domain to induce Bak-mediated permeabilization of liposomes and mitochondria, and determined the effect of wild type and mutant Puma on cell viability in a variety of cellular contexts. Results of this analysis demonstrate high affinity (KD = 26 ± 5 nM) binding of the Puma BH3 domain to purified Bak ex vivo, leading to Bak homo-oligomerization and membrane permeabilization. Mutations in Puma that inhibit (L141E/M144E/L148E) or enhance (M144I/A145G) Puma BH3 binding to Bak also produce corresponding alterations in Bak oligomerization, Bak-mediated membrane permeabilization and, in a cellular context, Bak-mediated killing. Collectively, these results provide strong evidence that Puma, like Bim, Noxa, and tBid, is able to act as a direct Bak activator.

Searching in mother nature for anti-cancer activity: anti-proliferative and pro-apoptotic effect elicited by green barley on leukemia/lymphoma cells

Green barley extract (GB) was investigated for possible anti-cancer activity by examining its anti-proliferative and pro-apoptotic properties on human leukemia/lymphoma cell lines. Our results indicate that GB exhibits selective anti-proliferative activity on a panel of leukemia/lymphoma cells in comparison to non-cancerous cells. Specifically, GB disrupted the cell-cycle progression within BJAB cells, as manifested by G2/M phase arrest and DNA fragmentation, and induced apoptosis, as evidenced by phosphatidylserine (PS) translocation to the outer cytoplasmic membrane in two B-lineage leukemia/lymphoma cell lines. The pro-apoptotic effect of GB was found to be independent of mitochondrial depolarization, thus implicating extrinsic cell death pathways to exert its cytotoxicity. Indeed, GB elicited an increase of TNF-α production, caspase-8 and caspase-3 activation, and PARP-1 cleavage within pre-B acute lymphoblastic leukemia Nalm-6 cells. Moreover, caspase-8 and caspase-3 activation and PARP-1 cleavage were strongly inhibited/blocked by the addition of the specific caspase inhibitors Z-VAD-FMK and Ac-DEVD-CHO. Furthermore, intracellular signaling analyses determined that GB treatment enhanced constitutive activation of Lck and Src tyrosine kinases in Nalm-6 cells. Taken together, these findings indicate that GB induced preferential anti-proliferative and pro-apoptotic signals within B-lineage leukemia/lymphoma cells, as determined by the following biochemical hallmarks of apoptosis: PS externalization, enhanced release of TNF-α, caspase-8 and caspase-3 activation, PARP-1 cleavage and DNA fragmentation Our observations reveal that GB has potential as an anti-leukemia/lymphoma agent alone or in combination with standard cancer therapies and thus warrants further evaluation in vivo to support these findings.

Apoptosis and Bcl-2 protein expression in human placenta over the course of normal pregnancy

Apoptosis plays a central role in organ development, homeostasis and immune defence in multicellular organisms and is strictly controlled in part by members of Bcl-2 family. The Bcl-2 is a pro-survival molecule identified through its involvement in B-cell lymphomas. The aim of the study was to evaluate the incidence of apoptosis in the human placenta at different stages of pregnancy and to correlate it further with Bcl-2 expression. A total of 96 placental samples from first trimester, mid-trimester and uncomplicated term pregnancies were collected (n = 32 + 32 + 32). M30 cyto death monoclonal antibody was used to identify apoptotic cells. The apoptosis index of first trimester placentae was 2.33 ± 1.70, mid- trimester was 1.77 ± 1.36 and term placenta was 1.15 ± 0.21. Bcl-2 protein was found immunolocalized in the cytoplasm of syncytiotrophoblast. Apoptosis index was significantly reduced in term cases as compared with first trimester (P < 0.002) and mid-trimester placentae (P = 0.01). On the contrary, Bcl-2 expression was significantly higher at term cases than in first trimester (P < 0.0001) and mid-trimester cases (P < 0.001). The present study divulges the importance of apoptosis in permitting normal physiological turnover of villous trophoblast and also exhibits the contribution of bcl-2 in maintaining syncytial integrity throughout normal pregnancy.

Wheat BAX inhibitor-1 contributes to wheat resistance to Puccinia striiformis

BAX inihibitor-1 (BI-1) is proposed to be a cell death suppressor conserved in both animals and plants. The ability of BI-1 genes to inhibit programmed cell death (PCD) has been well studied in animals, but the physiological importance of BI-1 in plant-microbe interactions remains unclear. This study characterized BI-1 from wheat infected by Puccinia striiformis f. sp. tritici (Pst). The deduced TaBI-1 protein contained a Bax inhibitor domain and seven transmembrane regions conserved among members of the BI-1 family. Transcription of TaBI-1 was detected in all wheat tissues tested (culms, roots, leaves, anthers, and spikelets). Furthermore, TaBI-1 exhibited positive transcriptional responses to Pst infection and abiotic stresses. Overexpression of TaBI-1 in tobacco blocked Bax-induced cell death. Silencing TaBI-1 in plants of a resistant wheat genotype converted a resistant reaction to a relatively susceptible reaction when inoculated with an avirulent pathotype of the pathogen, and increased the area per infection site, but the percentage of necrotic cells did not change significantly, indicating that TaBI-1, a negative cell death regulator, contributes to wheat resistance to stripe rust. These results provide a better understanding of the molecular mechanism of wheat resistance to stripe rust.

Apoptotic effects of curcumin on human osteosarcoma U2OS cells

OBJECTIVE

 Curcumin, an active ingredient derived from the rhizome of the plant, Curcuma longa, has antioxidant, anti-inflammatory and anti-cancer activities. The aims of this study were to examine whether curcumin can induce apoptosis in an osteosarcoma cell line.

METHODS

Curcumin-induced apoptosis in human osteosarcoma U2OS cells was investigated using morphological analysis, marked nuclear condensation and fragmentation of chromatin, which were observed by Hoechst 33258 staining and DNA ladder formation. The U2OS cells were treated with or without curcumin. Cell viability was assessed by the 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium (MTT) method. Cell-cycle, apoptosis and apoptosis-related proteins in U2OS cells were evaluated by flow cytometry and western blotting.

RESULTS

Curcumin showed growth inhibitory effects on U2OS cells in a dose-and time-dependent manner, inducing significant G1 arrest and apoptosis in U2OS cells. This curcumin-induced apoptosis in U2OS cells was accompanied by up-regulation of Bax, Bak, and p-Bad and down-regulation of Bcl-2, but no effect on the levels of Bcl-X(L) or Bad proteins was noted. Moreover, curcumin treatment resulted in a significant reduction of mitochondrial membrane potential and increase in the concentrations of mitochondrial cytochrome C and caspase-3.

CONCLUSION

Multiple molecular pathways are involved in curcumin-induced apoptosis of human U2OS cells. These include pro-and anti-apoptotic Bcl-2 family proteins, mitochondrial membrane potential, mitochondrial cytochrome C and caspase-3.

Prolongation of murine hybridoma cell survival in stationary batch culture by Bcl-xL expression

While the ectopic expression of the anti-apoptoticprotein Bcl-2 has been shown to significantly increaseboth cell viability and antibody production in batchculture, some cell lines are refractory to thesemanipulations. For example, the NS/O and theP3x63Ag8.653 murine myelomas, which express highendogenous levels of the Bcl-2 homologue Bcl-xL, areboth resistant to the anti-apoptotic effect of Bcl-2.This indicates that, in these cells, Bcl-2 and Bcl-xLmay be functionally redundant. In order to define therole which Bcl-xL plays in hybridoma cultures, we usedthe Sp2/0-Ag14 cell line. This murine hybridomaexpresses low levels of Bcl-xL and is highly sensitiveto apoptosis induction by cycloheximide (CHX) and byamino acid depletion. Bcl-xL-transfected Sp2/0-Ag14cells were more resistant than the wild type and theplasmid-containing cells to apoptosis induced by CHXand by glutamine depletion. Moreover, when compared tothe vector-transfected control, Bcl-xL-Sp2/0 cellsexhibited a substantial increase in viability instationary batch culture. Interestingly, Sp2/0-Ag14cells overexpressing Bcl-xL showed a growth behaviourthat was similar to the parent myeloma cell lineP3x63Ag8.653. Our results suggest that Bcl-xLexpression levels are sufficient to account for therelative robustness of some hybridoma cell lines instationary batch cultures.

Protection of hybridoma cells against apoptosis by a loop domain-deficient Bcl-xL protein

The ectopic expression of several members of the Bcl-2 family of anti-apoptotic proteins is a promising strategy to improve the viability of hybridoma cells in culture. However, the impact of post-translational modifications on the function of these proteins in murine hybridomas is unknown. To address this issue, the anti-apoptotic properties of a mutant of Bcl-xL devoid of the so-called "loop domain" (Bcl-xLtriangle up 46-83) were investigated using the Sp2/ O-Ag14 hybridoma model. Clones of Sp2/ O-Ag14 cells expressing Bcl-xLtriangle up 46-83 exhibited resistance against L-glutamine deprivation to similar levels than cells expressing the wild type protein. In contrast, protection against the cytotoxic effects of cycloheximide (CHX) was highly dependent on the level of expression of the Bcl-xLtriangle up 46-83 mutant. Analysis of the growth behaviour of the transfected cells showed that Bcl-xLtriangle up 46-83 was superior to the wild type protein in prolonging Sp2/ O-Agl4 cell viability in stationary batch culture. Furthermore, the prolongation of cell viability in batch culture was directly proportional to the level of expression of the mutated protein. Our results indicate that removal of the loop domain improves the anti-apoptotic activity of Bcl-xL in hybridoma cells grown in stationary batch culture.

Apoptosis and acute kidney injury

Improved mechanistic understanding of renal cell death in acute kidney injury (AKI) has generated new therapeutic targets. Clearly, the classic lesion of acute tubular necrosis is not adequate to describe the consequences of renal ischemia, nephrotoxin exposure, or sepsis on glomerular filtration rate. Experimental evidence supports a pathogenic role for apoptosis in AKI. Interestingly, proximal tubule epithelial cells are highly susceptible to apoptosis, and injury at this site contributes to organ failure. During apoptosis, well-orchestrated events converge at the mitochondrion, the organelle that integrates life and death signals generated by the BCL2 (B-cell lymphoma 2) protein family. Death requires the 'perfect storm' for outer mitochondrial membrane injury to release its cellular 'executioners'. The complexity of this process affords new targets for effective interventions, both before and after renal insults. Inhibiting apoptosis appears to be critical, because circulating factors released by the injured kidney induce apoptosis and inflammation in distant organs including the heart, lung, liver, and brain, potentially contributing to the high morbidity and mortality associated with AKI. Manipulation of known stress kinases upstream of mitochondrial injury, induction of endogenous, anti-apoptotic proteins, and improved understanding of the timing and consequences of renal cell apoptosis will inevitably improve the outcome of human AKI.

Potential role of CXCL10 in the induction of cell injury and mitochondrial dysfunction

Chemokines have been known to play a critical role in pathogenesis of chronic pancreatitis and acinar cell death. However, the role played by one of the CXC chemokines: CXCL10 in regulation of acinar cell death has remained unexplored. Hence, this study was designed to assess the role of CXCL10 promoting apoptosis in ex vivo cultured acinar cells. Primary human pancreatic acinar cell cultures were established and exposed to varying doses of CXCL10 for different time intervals. Apoptotic induction was evaluated by both qualitative as well as quantitative analyses. Various mediators of apoptosis were also studied by Western blotting, membrane potential (Psim) and ATP depletion in acinar cells. Analysis of apoptosis via DNA ladder and cell death detection - ELISA demonstrated that CXCL10 induced 3.9-fold apoptosis when administrated at an optimal dose of 0.1 mug of recombinant CXCL10 for 8 h. Quantitative analysis using FACS and dual staining by PI-annexin showed increased apoptosis (48.98 and 53.78% respectively). The involvement of upstream apoptotic regulators like pJNK, p38 and Bax was established on the basis of their increased expression of CXCL10. The change of Psim by 50% was observed in the presence of CXCL10 in treated acinar cells along with enhanced expression of Cytochrome C, apaf-1 and caspase 9/3 activation. In addition, ATP depletion was also noticed in CXCL10 stimulated acinar cells. CXCL10 induces cell death in human cultured pancreatic cells leading to apoptosis and DNA fragmentation via CXCR3 signalling. These signalling mechanisms may play an important role in parenchymal cell loss and injury in pancreatitis.

Gene expression in mouse preimplantation embryos affected by apoptotic inductor actinomycin D

The aim of this study was to test the effect of actinomycin D on the expression of selected genes and to elucidate possible components of its apoptotic pathway in mouse embryos. Selected mRNAs and Trp53 protein were examined in blastocysts cultured for 24 h in vitro with or without the presence of a high concentration of actinomycin D. In all tested genes, the relative quantities of mRNA were significantly lower in treated blastocysts than in controls. The mRNA quantities of H2afz, Actb, Bax, Bad and Bcl2 were reduced at a similar rate, but the decreases in Bcl2l2 and Trp53 mRNA were significantly greater. Treatment with actinomycin D also changed the ratio between the mRNA levels of some pro-apoptotic and anti-apoptotic genes: the Bad/Bcl2l2 and the Bax/Bcl2l2 ratios were on average 4.39 and 2.66 times higher in the treated embryos than in the controls, respectively. Generally, treatment led to developmental arrest and significant increase in the incidence of cells with typical apoptotic features. However, its effect on Trp53 protein expression was not significant. The results suggest that mechanisms beyond the apoptotic effect of actinomycin D might include specific changes in the expression of pro-apoptotic and anti-apoptotic genes, shifting the expression ratio in favor of the pro-apoptotic ones. The results also show that the role of Trp53 is probably not crucial in this apoptotic pathway.

Expression of HER-2 in MCF-7 breast cancer cells modulates anti-apoptotic proteins Survivin and Bcl-2 via the extracellular signal-related kinase (ERK) and phosphoinositide-3 kinase (PI3K) signalling pathways

Background

The oncoprotein HER-2 is over-expressed and/or has undergone gene amplification in between 20 to 30% of breast and ovarian cancers. HER-2 amplified breast cancer is associated with a poor prognosis and increased resistance to chemo- and hormonal therapy. Data supporting the transforming potential of HER-2 are irrefutable but the mechanism by which HER-2 contributes to this process is complex and a unified model of HER2-induced increased cell proliferation and survival has not emerged.

To understand the initial event(s) that take place by HER-2 over expression, we studied the effect of short term induction of HER-2 expression in the MCF7 breast cancer cell line.

Methods

We examined the modulation of apoptotic pathways by tetracycline-regulated HER-2 expression for 48 hrs in the MCF7 breast cancer cell line. Specific inhibitors were used to determine signalling pathways that are required for HER-2 induced up-regulation of survivin.

Results

Tetracycline regulated short term over expression of HER-2 in the MCF7 cell line increased the antiapoptotic proteins Bcl-2 and survivin levels. Significant increase of extracellular signal-related kinase (ERK) activation but not AKT1, AKT2 and STAT3 was observed in HER-2 over-expressing MCF7 cells. Specific inhibitors of ERK, and phosphoinositide-3 kinase (PI3K), inhibited the HER-2 induced up-regulation of survivin. We did not observe a change in survivin and NF-κB promoter activity in HER-2 expressing MCF7 cells.

Conclusion

Our results indicate that short term over expression of HER-2 up regulates antiapoptotic proteins Bcl-2 and survivin in MCF7 cells. We determined that survivin is up-regulated via ERK activation and PI3K signalling. Additionally we show that survivin up-regulation is not at transcriptional level. These data provide insight into the mechanism(s) by which induction of HER-2 over expression up-regulates survivin and Bcl-2 and identifies new targets for therapy of breast cancer.

Big wheel keeps on turning: apoptosome regulation and its role in chemoresistance

Apoptosis, a form of programmed cell death, enables organisms to maintain tissue homeostasis through deletion of extraneous cells and also serves as a means to eliminate potentially harmful cells. Numerous stress signals have been shown to engage the intrinsic pathway of apoptosis, with the release from mitochondria of proapoptotic factors such as cytochrome c and the subsequent formation of a cytosolic complex between apoptotic protease-activating factor-1 (Apaf-1) and procaspase-9, known as the apoptosome. Recent studies have led to the identification of an array of factors that control the formation and activation of the apoptosome under physiological conditions. Moreover, deregulation of apoptosome function has been documented in various forms of human cancer, and may play a role in both carcinogenesis and chemoresistance. We discuss how the apoptosome is regulated in normal and disease states, and how targeting of apoptosome-dependent, post-mitochondrial stages of apoptosis may serve as a rational approach to cancer treatment.

Actinomycin D upregulates proapoptotic protein Puma and downregulates Bcl-2 mRNA in normal peripheral blood lymphocytes

We have examined the ability of actinomycin D to induce apoptosis in human peripheral blood lymphocytes. Run-On assays were performed to specify the primary molecular damage, reverse transcription-PCR, Western blots and flow cytometry studies were performed to ascertain which proteins of the apoptosis machinery were affected to cause actinomycin D-induced cell death. Expression of 23 apoptosis-related genes was investigated. The down-regulation of ribosomal RNA synthesis caused by actinomycin D induced a mitochondria-dependent apoptosis. Although the expression of the majority of examined genes remained indifferent against actinomycin D activity, the cellular level of p53 protein increased, subsequently upregulating both Puma mRNA and protein. Puma-mediated mitochondrial apoptosis was accompanied by nucleolin cleavage and Bcl-2 mRNA destabilization. The stability of the cellular level of Bcl-2 protein independent of a mRNA decrease suggests that protection of Bcl-2 protein against proteasomal degradation can moderate the apoptotic process. In peripheral blood lymphocytes cultured in vitro, the apoptosis induced by a low concentration of actinomycin D (10 nmol/l) is dependent on p53 and Puma activation. This apoptotic pathway is demonstrated in peripheral blood lymphocytes for the first time. A different apoptotic pathway induced in peripheral blood lymphocytes using this drug has, however, been previously revealed by other authors. The combination of cell specificity and dose-dependent effects can likely play a decisive role in apoptosis observed in peripheral blood lymphocytes after genotoxic drug application.

PKB and the mitochondria: AKTing on apoptosis

Cellular homeostasis depends upon the strict regulation of responses to external stimuli, such as signalling cascades triggered by nutrients and growth factors, and upon cellular metabolism. One of the major molecules coordinating complex signalling pathways is protein kinase B (PKB), a serine/threonine kinase also known as Akt. The number of substrates known to be phosphorylated by PKB and its interacting partners, as well as our broad understanding of how PKB is implicated in responses to growth factors, metabolic pathways, proliferation, and cell death via apoptosis is constantly increasing. Activated by the insulin/growth factor-phosphatidylinositol 3-kinase (PI3K) cascade, PKB triggers events that promote cell survival and prevent apoptosis. It is also now widely accepted that mitochondria are not just suppliers of ATP, but that they participate in regulatory and signalling events, responding to multiple physiological inputs and genetic stresses, and regulate both cell proliferation and death. Thus, mitochondria are recognized as important players in apoptotic events and it is logical to predict some form of interplay with PKB. In this review, we will summarize mechanisms by which PKB mediates its anti-apoptotic activities in cells and survey recent developments in understanding mitochondrial dynamics and their role during apoptosis.

Bcl-2 cleavages at two adjacent sites by different caspases promote cisplatin-induced apoptosis

The protein encoded by bcl-2 proto-oncogene plays an important role in the mitochondria-mediated apoptotic pathway. Although the general role of Bcl-2 is anti-apoptotic, previous work showed that Bcl-2 fragments cleaved by caspases could promote apoptotic process. We report herein that Bcl-2 protein was cleaved to produce two fragments of around 23 kDa in human hepatocarcinoma BEL-7404 cells or in Bcl-2 overexpressing CHO cells induced by cisplatin. Treating cells with the general caspase inhibitor z-VAD-fmk blocked the induced cleavage of Bcl-2. Mutagenesis analyses showed that Bcl-2 was cleaved by caspases at two adjacent recognition sites in the loop domain (YEWD(31) decrease AGD(34) decrease V), which could be inhibited by caspase-8 and -3 inhibitors, respectively. Overexpression of the carboxyl terminal 23 kDa fragments increased the sensitivity of CHO cells to cisplatin-induced apoptosis. These results indicate that Bcl-2 can be cleaved into two close fragments by different caspases during cisplatin-induced apoptosis, both of which contribute to the acceleration of apoptotic process.

Mechanism of induction of pancreatic acinar cell apoptosis by hydrogen sulfide

The present study investigated the mechanism of mouse pancreatic acinar cell apoptosis induced by H2S in an in vitro system, using isolated pancreatic acini. Treatment of pancreatic acini with 10 μM NaHS (a donor of H2S) for 3 h caused phosphatidylserine externalization as shown by annexin V binding, an indicator of early stages of apoptosis. This treatment also resulted in the activation of the caspase cascade and major changes at the mitochondrial level. Caspase-3, -8, and -9 activities were stimulated by H2S treatment. Treatment with inhibitors of caspase-3, -8, and -9 significantly inhibited H2S-induced phosphatidylserine externalization as shown by reduced annexin V staining. The mitochondrial membrane potential was collapsed in H2S-treated acini as evidenced by fluorescence microscopy and quantitative analysis. Furthermore, the treatment of acini with H2S caused the release of cytochrome c by the mitochondria. To investigate the mechanism underlying pancreatic acinar cell apoptosis, we also characterized the protein expression of a range of molecules that are each known to influence the apoptotic pathway. Among proapoptotic proteins, Bax expression was activated in H2S-treated cells but not Bid, and the antiapoptotic proteins Bcl-XL and Bcl-2 did not show any activation in pancreatic acinar cell apoptosis. The death effector domain-containing protein Flip is downregulated in H2S-treated acini. These results demonstrate the induction of pancreatic acinar cell apoptosis in vitro by H2S and the involvement of both mitochondrial and death receptor pathways in the process of apoptosis.

Intestinal mucositis: the role of the Bcl-2 family, p53 and caspases in chemotherapy-induced damage

Intestinal mucositis occurs as a consequence of cytotoxic treatment through multiple mechanisms including induction of crypt cell death (apoptosis) and cytostasis. The molecular control of these actions throughout the gastrointestinal tract has yet to be fully elucidated; however, they are known to involve p53, the Bcl-2 family and caspases. This review will provide an overview of current research as well as identify areas where gaps in knowledge exist.

The p75(NTR) tumor suppressor induces cell cycle arrest facilitating caspase mediated apoptosis in prostate tumor cells

The p75 neurotrophin receptor (p75(NTR)) is a death receptor which belongs to the tumor necrosis factor receptor super-family of membrane proteins. This study shows that p75(NTR) retarded cell cycle progression by induced accumulation of cells in G0/G1 and a reduction in the S phase of the cell cycle. The rescue of tumor cells from cell cycle progression by a death domain deleted (DeltaDD) dominant-negative antagonist of p75(NTR) showed that the death domain transduced anti-proliferative activity in a ligand-independent manner. Conversely, addition of NGF ligand rescued retardation of cell cycle progression with commensurate changes in components of the cyclin/cdk holoenzyme complex. In the absence of ligand, p75(NTR)-dependent cell cycle arrest facilitated an increase in apoptotic nuclear fragmentation of the prostate cancer cells. Apoptosis of p75(NTR) expressing cells occurred via the intrinsic mitochondrial pathway leading to a sequential caspase-9 and -7 cascade. Since the death domain deleted dominant-negative antagonist of p75(NTR) rescued intrinsic caspase associated apoptosis in PC-3 cells, this shows p75(NTR) was integral to ligand independent induction of apoptosis. Moreover, the ability of ligand to ameliorate the p75(NTR)-dependent intrinsic apoptotic cascade indicates that NGF functioned as a survival factor for p75(NTR) expressing prostate cancer cells.

2-(4-methylphenyl)-1,3-selenazol-4-one induces apoptosis by different mechanisms in SKOV3 and HL 60 cells

We examined the ability of the synthetic selenium compound, 2-(4-methylphenyl)-1,3-selenazol-4-one (hereafter designated 3a), to induce apoptosis in a human ovarian cancer cell line (SKOV3) and a human leukemia cell line (HL-60). Flow cytometry showed that 3a treatment induced apoptosis in both cell lines to degrees comparable to that of the positive control, paclitaxel. Apoptosis was measured by PS externalization, DNA fragmentation and decreased mitochondrial membrane potential (MMP). However, analysis of the mechanism of action revealed differences between the responses of the two cell lines. Treatment with 3a arrested the cell cycle and induced caspase-3 activation in HL-60 cells, but not in SKOV3 cells. In contrast, 3a treatment induced apoptosis through translocation of AIF, a novel pro-apoptotic protein, in SKOV3 cells, but not in HL-60 cells. Collectively, our data demonstrated that 3a induced apoptosis in both cell lines, but via different action mechanisms.

Apoptosis: a basic biological phenomenon with wide-ranging implications in human disease

Apoptosis is a highly regulated process of cell deletion and plays a fundamental role in the maintenance of tissue homeostasis in the adult organism. Numerous studies in recent years have revealed that apoptosis is a constitutive suicide programme expressed in most, if not all cells, and can be triggered by a variety of extrinsic and intrinsic signals. Many human diseases can be attributed directly or indirectly to a derangement of apoptosis, resulting in either cell accumulation, in which cell eradication or cell turnover is impaired, or cell loss, in which the apoptotic programme is inadvertently triggered. In addition, defective macrophage engulfment and degradation of cell corpses may also contribute to a dysregulation of tissue homeostasis. An increased understanding of the signalling pathways that govern the execution of apoptosis and the subsequent clearance of dying cells may thus yield novel targets for therapeutic intervention in a wide range of human maladies.

Developmental shift in the apostat: comparison of neurones and astrocytes

The intrinsic pathway of apoptosis was investigated in cell-free extracts of neurones and astrocytes at various stages of maturation. Neuronal extracts were activated 65-fold after 3 days, 9-fold after 7 days, and were not activated after 10 days in culture. In contrast, astrocyte extracts were activated to a similar extent at all stages, up to 60 days in culture. The co-incubation of neuronal and astrocyte extracts followed by addition of cytochrome c/2'-deoxyadenosine 5'-triphosphate led to a 40-fold activation, suggesting that the development-associated neuronal shift does not involve the appearance of a dominant inhibitor, but rather downregulation of some key component(s) involved in caspase activation.

The roles of Bcl-xL in modulating apoptosis during development of Xenopus laevis

Background

Apoptosis is a common and essential aspect of development. It is particularly prevalent in the central nervous system and during remodelling processes such as formation of the digits and in amphibian metamorphosis. Apoptosis, which is dependent upon a balance between pro- and anti-apoptotic factors, also enables the embryo to rid itself of cells damaged by gamma irradiation. In this study, the roles of the anti-apoptotic factor Bcl-x_L in protecting cells from apoptosis were examined in Xenopus laevis embryos using transgenesis to overexpress the XR11 gene, which encodes Bcl-x_L. The effects on developmental, thyroid hormone-induced and γ-radiation-induced apoptosis in embryos were examined in these transgenic animals.

Results

Apoptosis was abrogated in XR11 transgenic embryos. However, the transgene did not prevent the apoptotic response of tadpoles to thyroid hormone during metamorphosis. Post-metamorphic XR11 frogs were reared to sexual maturity, thus allowing us to produce second-generation embryos and enabling us to distinguish between the maternal and zygotic contributions of Bcl-x_L to the γ-radiation apoptotic response. Wild-type embryos irradiated before the mid-blastula transition (MBT) underwent normal cell division until reaching the MBT, after which they underwent massive, catastrophic apoptosis. Over-expression of Bcl-x_L derived from XR11 females, but not males, provided partial protection from apoptosis. Maternal expression of XR11 was also sufficient to abrogate apoptosis triggered by post-MBT γ-radiation. Tolerance to post-MBT γ-radiation from zygotically-derived XR11 was acquired gradually after the MBT in spite of abundant XR11 protein synthesis.

Conclusion

Our data suggest that Bcl-x_L is an effective counterbalance to proapoptotic factors during embryonic development but has no apparent effect on the thyroid hormone-induced apoptosis that occurs during metamorphosis. Furthermore, post-MBT apoptosis triggered by irradiation before the MBT could only be restrained by maternal expression of Bcl-x_L. Although maternal expression of XR11 was sufficient to abrogate apoptosis triggered by post-MBT γ-radiation, radiation tolerance from zygotically-derived XR11 was acquired gradually, indicating that synthesis of XR11 protein is not sufficient to prevent apoptosis. Thus, repression of radiation-induced apoptosis by overexpression of Bcl-x_L during embryonic development depends upon the timing of its expression and post-translational events that enable the protein to become effective.

L'apoptose : bases fondamentales et applications médicales

Apoptosis has become a most popular concept of cell death. What makes apoptosis particularly exciting for medicine is that its dysfunctions play a central role in the pathogenesis of several human diseases. This review summarizes the considerable knowledge about the cell death pathways. The purpose of this article is to provide a background of relevance to clinicians on apoptosis, and the rationale for future therapeutic interventions directed toward the apoptotic machinery.

Changes of Plasma Membrane Properties in a Human Pre-T Cell Line Undergoing Apoptosis

A variety of cellular functions are modulated by the physical properties of the cell membrane, and the modification of intracellular transfer, resulting from loss of membrane integrity, may contribute toward setting the cell onto the pathway of apoptosis. Apoptosis in lymphoid cells can be induced in different ways and biochemical modifications occur at an early phase of cell death, while the morphological features of apoptosis are evident later. We previously reported that DMSO is an efficient apoptosis-inducing factor in the human RPMI-8402 pre-T cell line. The aim of the present study was to verify the effect of DMSO on the plasma membrane fluidity, the intracellular calcium concentration and the phosphodiesterase activity in DMSO-induced apoptosis. Our results show a modification of membrane fluidity associated with an increase of intracellular Ca(2+) concentration. Moreover, we demonstrate that these modifications are related to a decrease in the phosphodiesterase (PDE) activity. The correlation between the proceedings of added DMSO and the induction of apoptosis will provide significant information regarding the first part of the apoptotic process.

Menstrual-like breakdown and apoptosis in human endometrial explants

BACKGROUND

Apoptosis occurs in late secretory and menstrual human endometrium and is thought to play an important role in endometrial physiology. Menstrual-like breakdown has been observed in vitro in endometrial explants. The purpose of this study was to assess the role of apoptosis in menstrual-like breakdown in human endometrial explants.

METHODS

Human endometrial tissue was obtained during the mid-secretory phase and cultured with or without estrogen and progesterone. The occurrence of breakdown was assessed by histology. Apoptosis was determined by gel electrophoresis for the detection of DNA fragmentation and by immunohistochemistry using the M30 CytoDEATH and anti-cleaved caspase-3 (CASP3) antibodies for the detection of caspase activity. Expression of BCL2 and BAX was quantified using real-time PCR analysis.

RESULTS

Apoptosis occurred in human endometrial explants at all time-points studied. Cleaved CASP3 and M30 antigen expression increased in all explants, suggesting the involvement of CASP3 in the apoptosis. Low BCL2:BAX ratios were observed in all samples when compared with pre-culture controls. Estradiol and progesterone supplementation of the culture media reduced or eliminated menstrual-like breakdown but did not affect the degree of apoptosis observed.

CONCLUSIONS

The apoptosis observed in endometrium during the late secretory phase and menstrual phase does not appear to be mechanistically related to the tissue breakdown but rather may be involved in the impending remodelling that occurs in the endometrium in the transition from secretory to proliferative phase following the menses.

Epstein-Barr virus-encoded latent membrane protein 1 promotes stress-induced apoptosis upstream of caspase-2-dependent mitochondrial perturbation

Previous studies have shown that Epstein-Barr virus (EBV)-encoded latent membrane protein 1 (LMP1) enhances etoposide-induced apoptosis in epithelial cells. Our study was undertaken to further dissect the modulation of tumor cell apoptosis by this viral protein. Using an inducible system of LMP1 expression in HeLa cells, we show herein that etoposide-triggered apoptosis, as evidenced by nuclear condensation and caspase-3 activation, is enhanced by LMP1. LMP1 also potentiates etoposide-induced processing and activation of caspase-2 in this model and enhances the dissipation of mitochondrial transmembrane potential and the release of cytochrome c in response to etoposide. Moreover, cisplatin-triggered activation of caspases 2 and 3 is potentiated upon expression of LMP1. A similar LMP1-mediated enhancement of cisplatin-induced caspase activation was seen upon stable transfection of wild-type LMP1 into the nasopharyngeal carcinoma cell line, TW03. Finally, using deletion mutants of LMP1 to determine the region of LMP1 required for apoptosis potentiation, we found that amino acids 350-386 (located within the CTAR2 domain) were responsible for sensitizing cells to cisplatin. We conclude that LMP1-dependent potentiation of stress-induced apoptosis occurs at an early step in the apoptosis cascade, upstream of the activation of caspase-2, and involves the C-terminal signaling domain of LMP1. These findings could have important ramifications for the treatment of EBV-associated malignancies of epithelial origin, including nasopharyngeal carcinoma.

On the antioxidant mechanisms of Bcl-2: a retrospective of NF-kappaB signaling and oxidative stress

Antioxidant and prooxidant signaling pathways are emanating as major players in, and regulators of, cell death and apoptosis. Redox conception of the critical role of oxidative stress in determining cell fate is being established-a foundation that craves deeper than the basic understanding of physiochemical interactions to extend beyond that into the realms of deciphering the molecular codes implicated with apoptosis. The proto-oncogene Bcl-2 is no stranger being a major player and decoder in controlling apoptosis, ostensibly via the regulation of redox equilibrium and disequilibrium. One of those potential mechanisms exhibited by Bcl-2 is its ability to counteract the detrimental effects of cell damage caused by free radicals, thereby gaining its well-known property of being an antioxidant. But the question is: what are the molecular mechanisms involved with the antioxidant role of Bcl-2 in the face of cell damage and apoptosis? Currently, a stance is being upheld in that the Bcl-2 antioxidant efficacy should be weighed against its ability to manipulate transcriptional control, through the regulation of specific transcription factors. NF-kappaB is no doubt one of the best candidates when it comes to the arena of oxidative stress, inflammation, and apoptosis. Therein, current themes in the burgeoning antioxidant role of Bcl-2 are exposed within the context of transcriptional control of NF-kappaB, thereby holding potential avenues for alleviating therapeutic approaches in the regulation of apoptosis.

Cadmium-induced apoptosis through the mitochondrial pathway in rainbow trout hepatocytes: involvement of oxidative stress

Cadmium (Cd) induces oxidative stress and apoptosis in trout hepatocytes. We therefore investigated the involvement of the mitochondrial pathway in the initiation of apoptosis and the possible role of oxidative stress in that process. This study demonstrates that hepatocyte exposure to Cd (2, 5 and 10 microM) triggers significant caspase-3, but also caspase-8 and -9 activation in a dose-dependent manner. Western-blot analysis of hepatocyte mitochondrial and cytosolic fractions revealed that cytochrome c (Cyt c) was released in the cytosol in a dose-dependent manner, whereas the pro-apoptotic protein Bax was redistributed to mitochondria after 24 and 48 h exposure. We also found that the expression of anti-apoptotic protein Bcl-xL, known to be regulated under mild oxidative stress to protect cells from apoptosis, did not change after 3 and 6 h exposure to Cd, then increased after 24 and 48 h exposure to 10 microM Cd. In the second part of this work, two antioxidant agents, 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) (100 microM) and N-acetylcysteine (NAC, 100 microM) were used to determine the involvement of reactive oxygen species (ROS) in Cd-induced apoptosis. Simultaneously exposing trout hepatocytes to Cd and TEMPO or NAC significantly reduced caspase-3 activation after 48 h and had a suppressive effect on caspase-8 and -9 also, mostly after 24 h. Lastly, the presence of either one of these antioxidants in the treatment medium also attenuated Cd-induced Cyt c release in cytosol and the level of Bax in the mitochondria after 24 and 48 h, while high Bcl-xL expression was observed. Taken together, these data clearly evidenced the key role of mitochondria in the cascade of events leading to trout hepatocyte apoptosis in response to Cd and the relationship that exists between oxidative stress and cell death.

Pivotal role of the cell death factor BNIP3 in ceramide-induced autophagic cell death in malignant glioma cells

The sphingolipid ceramide has been recognized as an important second messenger implicated in regulating diverse signaling pathways especially for apoptosis. Very little is known, however, about the molecular mechanisms underlying nonapoptotic cell death induced by ceramide. In the present study, we first demonstrate that ceramide induces nonapoptotic cell death in malignant glioma cells. The cell death was accompanied by several specific features characteristic of autophagy: presence of numerous autophagic vacuoles in the cytoplasm, development of the acidic vesicular organelles, autophagosome membrane association of microtubule-associated protein light chain 3 (LC3), and a marked increase in expression levels of two forms of LC3 protein (LC3-I and LC3-II). We additionally demonstrate that ceramide decreases mitochondrial membrane potential and activates the transcription of death-inducing mitochondrial protein, BNIP3, resulting in increased expression levels of its mRNA and protein in malignant glioma cells. Moreover, tumor cells transfected with BNIP3 gene undergo autophagy in the absence of ceramide. These results suggest that ceramide induces autophagic cell death in malignant glioma cells via activation of BNIP3. This study adds a new concept to characterize the pathways by which ceramide acts to induce nonapoptotic autophagic cell death in malignant gliomas.

Kostmann syndrome: severe congenital neutropenia associated with defective expression of Bcl-2, constitutive mitochondrial release of cytochrome c, and excessive apoptosis of myeloid progenitor cells

Kostmann syndrome, or severe congenital neutropenia (SCN), is an autosomal recessive disorder of neutrophil production. To investigate the potential role of apoptosis in SCN, bone marrow aspirates and biopsies were obtained from 4 patients belonging to the kindred originally described by Kostmann and 1 patient with SCN of unknown inheritance. An elevated degree of apoptosis was observed in the bone marrow of these patients, and a selective decrease in B-cell lymphoma-2 (Bcl-2) expression was seen in myeloid progenitor cells. Furthermore, in vitro apoptosis of bone marrow-derived Kostmann progenitor cells was increased, and mitochondrial release of cytochrome c was detected in CD34+ and CD33+ progenitors from patients, but not in controls. Administration of granulocyte colony-stimulating factor (G-CSF) restored Bcl-2 expression and improved survival of myeloid progenitor cells. In addition, cytochrome c release was partially reversed upon incubation of progenitor cells with G-CSF. In sum, these studies establish a role for mitochondria-dependent apoptosis in the pathogenesis of Kostmann syndrome and yield a tentative explanation for the beneficial effect of growth factor administration in these patients. (Blood. 2004;103:3355-3361)

Apoptosis and macrophage clearance of neutrophils: regulation by reactive oxygen species

Inflammation is a beneficial host response to foreign challenge involving numerous soluble factors and cell types, including polymorphonuclear granulocytes or neutrophils. Programmed cell death (apoptosis) of neutrophils has been documented in vitro as well as in vivo, and is thought to be important for the resolution of inflammation, as this process allows for engulfment and removal of senescent cells prior to their necrotic disintegration. Studies in recent years have begun to unravel the mechanism of macrophage clearance of apoptotic cells, and evidence has accrued for a critical role of externalization and oxidation of plasma membrane phosphatidylserine, and its subsequent recognition by macrophage receptors, in this process. Activated neutrophils generate vast amounts of reactive oxygen species for the purpose of killing ingested micro-organisms, and these reactive metabolites may also modulate the life-span, as well as the clearance, of the neutrophil itself. This review aims to address the latter topic, as well as to summarize current knowledge on the molecular mechanisms of neutrophil apoptosis and macrophage clearance of these cells at the site of inflammation.

AMPA-induced dark cell degeneration of cerebellar Purkinje neurons involves activation of caspases and apparent mitochondrial dysfunction

Cerebellar Purkinje neurons (PNs) are selectively vulnerable to AMPA (alpha-amino-3-hydroxy-5-methyl-4-isoxazolepriopionic acid)-induced delayed neurotoxicity known as dark cell degeneration (DCD) that is expressed as cytoplasmic and nuclear condensation, neuron shrinkage, and failure of physiology. The present study was initiated to determine whether AMPA-receptor-induced DCD in PNs is associated with Bax translocation to the mitochondria, cytochrome C release from the mitochondria, changes in mitochondrial potential, and activation of representative initiator and executor caspases that include caspase-9, caspase-3, and caspase-7. AMPA consistently and rapidly hyperpolarized mitochondria as reflected by an increase in MitoTracker Red CMS Ros fluorescence. Increases in Bax immunoreactivity were quantitatively and temporally variable and Bax failed to localize to mitochondria. Additionally, we observed a marked increase in immunoreactivity of cytochrome C although its release from mitochondria was not apparent. Mitochondrial membrane hyperpolarization and increases in cytochrome C immunoreactivity preceded caspase activation. Immunohistochemical analyses revealed the active form of caspases-3 and -9 were markedly and significantly increased in PNs following 30 microM AMPA, and caspase-9 activation preceded caspase-3. Increases in active caspase-7 immunoreactivity were less frequently encountered in PNs. Thus DCD shares some characteristics of apoptotic programmed cell death, but lacks typical mitochondrial pathophysiology associated with classic apoptosis. These findings suggest that AMPA-induced DCD is a form of active PCD that lies on a spectrum between classical apoptosis and passive necrosis.

Mechanism of taxol-induced apoptosis in human SKOV3 ovarian carcinoma cells

Taxol is extensively used clinically for chemotherapy of patients with ovarian, breast, and lung cancer. Although taxol induces apoptosis of cancer cells, its exact mechanism of action is not yet known. To determine the mechanism of action of taxol in ovarian cancer, we tested the effects of the drug, on the human ovarian carcinoma cell line, SKOV3. We observed that taxol-induced apoptosis of these cells by phosphatidylserine (PS) externalization and DNA fragmentation. While treatment of cells with taxol resulted in bcl-2 phosphorylation and mitochondrial depolarization, cytochrome c was not released and pro-caspase-3 was not activated. Treatment of SKOV3 cells with taxol, however, resulted in the translocation of AIF from the mitochondria to the nucleus via the cytosol. Taken together, these findings suggest that in SKOV3 cells, taxol induces caspase-independent AIF-dependent apoptosis.

Cell death and growth arrest in response to photodynamic therapy with membrane-bound photosensitizers

Photodynamic therapy (PDT) is a treatment for cancer and for certain benign conditions that is based on the use of a photosensitizer and light to produce reactive oxygen species in cells. Many of the photosensitizers currently used in PDT localize in different cell compartments such as mitochondria, lysosomes, endoplasmic reticulum and generate cell death by triggering necrosis and/or apoptosis. Efficient cell death is observed when light, oxygen and the photosensitizer are not limiting ("high dose PDT"). When one of these components is limiting ("low dose PDT"), most of the cells do not immediately undergo apoptosis or necrosis but are growth arrested with several transduction pathways activated. This commentary will review the mechanism of apoptosis and growth arrest mediated by two important PDT agents, i.e. pyropheophorbide and hypericin.

Are the molecular strategies that control apoptosis conserved in bacteria?

The Staphylococcus aureus cid and lrg operons have been shown to encode putative membrane proteins that are involved in the regulation of murein hydrolase activity and penicillin tolerance. Cid proteins enhance murein hydrolase activity and penicillin sensitivity, whereas Lrg proteins have an inhibitory effect on these processes. It has been proposed that the Cid and Lrg proteins function in a way analogous to bacteriophage-encoded holins and antiholins, respectively, which control the timing of bacteriophage-induced lysis. This article explores the possibility that the Cid-Lrg regulatory system controls bacterial programmed cell death using a molecular strategy that it is functionally analogous to that mediated by the eukaryotic Bcl-2 family of apoptosis regulatory proteins.

Phosphorylation of the pro-apoptotic protein Bim in lymphocytes is associated with protection from apoptosis

Bim is a pro-apoptotic member of the Bcl-2 protein family. Bim has three isoforms, EL, L, and S, of which the EL form is the least cytotoxic. We show here that Bim is serine phosphorylated in lymphocytes, predominantly on the EL form. Withdrawal of IL-2 from IL-2-dependent T lymphocytes or culture of thymocytes leads to reduced Bim phosphorylation and apoptosis induction. This decrease in Bim phosphorylation occurs when most cells in culture are still viable, indicating that reduction of Bim phosphorylation may be an early event in apoptosis signaling of lymphocytes.

Mitochondria-mediated caspase-independent apoptosis induced by cadmium in normal human lung cells

Cadmium, a well-known environmental hazard, has caused serious health problems in humans and animals. Accumulating evidence suggests the cadmium toxicity is mediated by oxidative stress-induced cell death. However, the molecular signaling underlying cadmium-induced apoptosis remains unclear. In this study, we demonstrate here that cadmium induced mixed types of cell death including primary apoptosis (early apoptosis), secondary necrosis (late apoptosis), and necrosis in normal human lung cells, MRC-5, as revealed by chromatin condensation, phosphatidylserine (PS) externalization, and hypodiploid DNA content. The total apoptotic cells reached a plateau of around 40.0% after 24 h exposure of 100 microM cadmium. Pretreatment with Z-Val-Ala-Asp-fluoromethylketone (Z-VAD-fmk), a broad spectrum of caspase inhibitor, could not rescue apoptotic cells from cadmium toxicity. Coincidently, we failed to detect the activation of pro-caspase-3 and cleavage of PARP by immunoblot, which implies the apoptogenic activity of cadmium in MRC-5 cells is caspase-independent. JC-1 staining also indicated that mitochondrial depolarization is a prelude to cadmium-induced apoptosis, which was accompanied by a translocation of caspase-independent pro-apoptotic factor apoptosis-inducing factor (AIF) into the nucleus as revealed by the immunofluorescence assay. In summary, this study demonstrated for the first time that cadmium induced a caspase-independent apoptotic pathway through mitochondria-mediated AIF translocation into the nucleus.

Effect of trans-resveratrol on signal transduction pathways involved in paclitaxel-induced apoptosis in human neuroblastoma SH-SY5Y cells

trans-Resveratrol (3,4',5-trihydroxystilbene) is able to significantly reduce paclitaxel-induced apoptosis in the human neuroblastoma (HN) SH-SY5Y cell line, acting on several cellular signaling pathways that are involved in paclitaxel-induced apoptosis. trans-Resveratrol reverses phosphorylation of Bcl-2 induced by paclitaxel and concomitantly blocks Raf-1 phosphorylation, also observed after paclitaxel exposure, thus suggesting that Bcl-2 inactivation may be dependent on the activation of the Raf/Ras cascade. trans-Resveratrol also reverses the sustained phosphorylation of JNK/SAPK, which specifically occurs after paclitaxel exposure.Overall, our observations demonstrate that (a) the toxic action of paclitaxel on neuronal-like cells is not only related to the effect of the drug on tubulin, but also to its capacity to activate several intracellular pathways leading to inactivation of Bcl-2, thus causing cells to die by apoptosis, (b) trans-resveratrol significantly reduces paclitaxel-induced apoptosis by modulating the cellular signaling pathways which commit the cell to apoptosis.

Apoptosis, proliferation, differentiation: in search of the order

In search of the order, we are tempted to universally link cell death, proliferation, differentiation, and senescence. Current models (classical, conflicting signal and quantitative signal models) are restricted, precisely because they attempt to hardware a plethora of end-points of cellular responses. By defining each cellular process in molecular term, one can disconnect proliferation (CDK activation), apoptosis (caspase activation), and differentiation (tissue function genes expression), even though these responses are linked by upstream signal transduction pathways. These ambivalent pathways (e.g. mitogen-activated pathways) simultaneously transduce opposite signals (for growth arrest and cycling, for cell death and survival), which are ultimately translated in all possible combinations of cellular responses. When depicted in multidimensional axis, this universal model may also include invasiveness, senescence, metastatic and angiogenic responses and even such integral characteristics as malignant transformation.