Mitochondrial involvement in aspirin-induced apoptosis in yeast

Whole and Purified Aqueous Extracts of Nigella sativa L. Seeds Attenuate Apoptosis and the Overproduction of Reactive Oxygen Species Triggered by p53 Over-Expression in the Yeast Saccharomyces cerevisiae

Plants are an important source of pharmacologically active compounds. In the present work, we characterize the impact of black cumin (Nigella sativa L.) aqueous extracts on a yeast model of p53-dependent apoptosis. To this end, the Saccharomyces cerevisiae recombinant strain over-expressing p53 was used. The over-expression of p53 triggers the expression of apoptotic markers: the externalization of phosphatidylserine, mitochondrial defect associated with cytochrome-c release and the induction of DNA strand breaks. These different effects were attenuated by Nigella sativa L. aqueous extracts, whereas these extracts have no effect on the level of p53 expression. Thus, we focus on the anti-apoptotic molecules present in the aqueous extract of Nigella sativa L. These extracts were purified and characterized by complementary chromatographic methods. Specific fluorescent probes were used to determine the effect of the extracts on yeast apoptosis. Yeast cells over-expressing p53 decrease in relative size and have lower mitochondrial content. The decrease in cell size was proportional to the decrease in mitochondrial content and of mitochondrial membrane potential (ΔΨm). These effects were prevented by the purified aqueous fraction obtained by fractionation with different columns, named C4 fraction. Yeast cell death was also characterized by reactive oxygen species (ROS) overproduction. In the presence of the C4 fraction, ROS overproduction was strongly reduced. We also noted that the C4 fraction promotes the cell growth of control yeast cells, which do not express p53, supporting the fact that this purified extract acts on cellular mediators activating cell proliferation independently of p53. Altogether, our data obtained on yeast cells over-expressing p53 demonstrate that anti-apoptotic molecules targeting p53-induced apoptosis associated with mitochondrial dysfunction and ROS overproduction are present in the aqueous extracts of Nigella seeds and in the purified aqueous C4 fraction.

Aspirin damages the cell wall of Saccharomyces cerevisiae by inhibiting the expression and activity of dolichol-phosphate mannose synthase 1

Aspirin is a commonly used anti-inflammatory, analgesic and antithrombotic drug. It has attracted attention due to its potential antifungal therapeutic effect; however, the molecular mechanism is poorly understood. Here, the effects of aspirin on the cell wall of Saccharomyces cerevisiae were explored. We observed by scanning electron microscopy that aspirin could damage the cell wall ultrastructure. Meanwhile, a cellular surface hydrophobicity (CSH) assay showed that aspirin increased the hydrophobicity of the yeast cell surface. A drug sensitivity assay indicated that the overexpression of dolichol phosphate mannose synthase 1 (DPM1) reversed the cell wall damage and decreased the CSH induced by aspirin. Importantly, aspirin decreased the expression and enzyme activity of DPM1 in S. cerevisiae. Molecular docking results demonstrated that aspirin could directly bind to the Ser141 site of DPM1. Similarly, we found that aspirin damaged the cell wall and inhibited the expression of DPM1 in Candida albicans. These findings improve the current understanding of the action mode of aspirin and provide new strategies for antifungal drug design.

Aspirin impairs acetyl-coenzyme A metabolism in redox-compromised yeast cells

Aspirin is a widely used anti-inflammatory and antithrombotic drug also known in recent years for its promising chemopreventive antineoplastic properties, thought to be mediated in part by its ability to induce apoptotic cell death. However, the full range of mechanisms underlying aspirin's cancer-preventive properties is still elusive. In this study, we observed that aspirin impaired both the synthesis and transport of acetyl-coenzyme A (acetyl-CoA) into the mitochondria of manganese superoxide dismutase (MnSOD)-deficient Saccharomyces cerevisiae EG110 yeast cells, but not of the wild-type cells, grown aerobically in ethanol medium. This occurred at both the gene level, as indicated by microarray and qRT-PCR analyses, and at the protein level as indicated by enzyme assays. These results show that in redox-compromised MnSOD-deficient yeast cells, but not in wild-type cells, aspirin starves the mitochondria of acetyl-CoA and likely causes energy failure linked to mitochondrial damage, resulting in cell death. Since acetyl-CoA is one of the least-studied targets of aspirin in terms of the latter's propensity to prevent cancer, this work may provide further mechanistic insight into aspirin's chemopreventive behavior with respect to early stage cancer cells, which tend to have downregulated MnSOD and are also redox-compromised.

Antagonism between salicylate and the cAMP signal controls yeast cell survival and growth recovery from quiescence

Aspirin and its main metabolite salicylate are promising molecules in preventing cancer and metabolic diseases. S. cerevisiae cells have been used to study some of their effects: (i) salicylate induces the reversible inhibition of both glucose transport and the biosyntheses of glucose-derived sugar phosphates, (ii) Aspirin/salicylate causes apoptosis associated with superoxide radical accumulation or early cell necrosis in MnSOD-deficient cells growing in ethanol or in glucose, respectively. So, treatment with (acetyl)-salicylic acid can alter the yeast metabolism and is associated with cell death. We describe here the dramatic effects of salicylate on cellular control of the exit from a quiescence state. The growth recovery of long-term stationary phase cells was strongly inhibited in the presence of salicylate, to a degree proportional to the drug concentration. At high salicylate concentration, growth reactivation was completely repressed and associated with a dramatic loss of cell viability. Strikingly, both of these phenotypes were fully suppressed by increasing the cAMP signal without any variation of the exponential growth rate. Upon nutrient exhaustion, salicylate induced a premature lethal cell cycle arrest in the budded-G2/M phase that cannot be suppressed by PKA activation. We discuss how the dramatic antagonism between cAMP and salicylate could be conserved and impinge common targets in yeast and humans. Targeting quiescence of cancer cells with stem-like properties and their growth recovery from dormancy are major challenges in cancer therapy. If mechanisms underlying cAMP-salicylate antagonism will be defined in our model, this might have significant therapeutic implications.

Similar environments but diverse fates: Responses of budding yeast to nutrient deprivation

Diploid budding yeast (Saccharomyces cerevisiae) can adopt one of several alternative differentiation fates in response to nutrient limitation, and each of these fates provides distinct biological functions. When different strain backgrounds are taken into account, these various fates occur in response to similar environmental cues, are regulated by the same signal transduction pathways, and share many of the same master regulators. I propose that the relationships between fate choice, environmental cues and signaling pathways are not Boolean, but involve graded levels of signals, pathway activation and master-regulator activity. In the absence of large differences between environmental cues, small differences in the concentration of cues may be reinforced by cell-to-cell signals. These signals are particularly essential for fate determination within communities, such as colonies and biofilms, where fate choice varies dramatically from one region of the community to another. The lack of Boolean relationships between cues, signaling pathways, master regulators and cell fates may allow yeast communities to respond appropriately to the wide range of environments they encounter in nature.

Menadione-induced caspase-dependent programmed cell death in the green chlorophyte Chlamydomonas reinhardtii

Menadione, a quinone that undergoes redox cycles leading to the formation of superoxide radicals, induces programmed cell death (PCD) in animals and plants. In this study, we investigated whether the unicellular green alga Chlamydomonas reinhardtii P.A.Dangeard is capable of executing PCD upon exposure to menadione stress. We report here, the morphological, molecular, and biochemical changes after menadione exposure of C. reinhardtii cells. The effect of menadione on cell death has been shown to be dose-dependent; 5-100 μM menadione causes 20%-46% cell death, respectively. It appears that growth is inhibited with the concomitant degradation of the photosynthetic pigments and by a decrease in the photosynthetic capacity. Being an oxidative stress, we found an H2 O2 burst within 15 min of menadione exposure, followed by an increase in antioxidant enzyme (superoxide dismutase [SOD], catalase [CAT], and ascorbate peroxidase [APX]) activities. In parallel, RT-PCR was performed for transcript analyses of Mn-SOD, CAT, and APX. Our results clearly revealed that expression of these genes were up-regulated upon menadione exposure. Furthermore, classical hallmarks of PCD such as alteration of mitochondrial membrane potential, significant increase in caspase-3-like DEVDase activity, cleavage of poly (ADP) ribose polymerase (PARP)-1-like enzyme, and DNA fragmentation as detected by terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay and oligosomal DNA fragmentation were observed. Moreover, antibodies against a mammalian active caspase-3 shared epitopes with a caspase-3-like protein of ~17 kDa; its pattern of expression and activity correlated with the onset of cell death. To the best of our knowledge, this is the first report on menadione-induced PCD through a mitochondrian-caspase protease pathway in an algal species.

Phenoptosis in yeasts

The current view on phenoptosis and apoptosis as genetic programs aimed at eliminating potentially dangerous organisms and cells, respectively, is given. Special emphasis is placed on apoptosis (phenoptosis) in yeasts: intracellular defects and a plethora of external stimuli inducing apoptosis in yeasts; distinctive morphological and biochemical hallmarks accompanying apoptosis in yeasts; pro- and antiapoptotic factors involved in yeast apoptosis signaling; consecutive stages of apoptosis from external stimulus to the cell death; a prominent role of mitochondria and other organelles in yeast apoptosis; possible pathways for release of apoptotic factors from the intermembrane mitochondrial space into the cytosol are described. Using some concrete examples, the obvious physiological importance and expediency of altruistic death of yeast cells is shown. Poorly known aspects of yeast apoptosis and prospects for yeast apoptosis study are defined.

Crambescidin-816 acts as a fungicidal with more potency than crambescidin-800 and -830, inducing cell cycle arrest, increased cell size and apoptosis in Saccharomyces cerevisiae

In this paper, we show the effect of crambescidin-816, -800, and -830 on Saccharomyces cerevisiae viability. We determined that, of the three molecules tested, crambescidin-816 was the most potent. Based on this result, we continued by determining the effect of crambescidin-816 on the cell cycle of this yeast. The compound induced cell cycle arrest in G2/M followed by an increase in cell DNA content and size. When the type of cell death was analyzed, we observed that crambescidin-816 induced apoptosis. The antifungal effect indicates that crambescidins, and mostly crambescidin-816, could serve as a lead compound to fight fungal infections.

Aspirin-induced apoptosis of yeast cells is associated with mitochondrial superoxide radical accumulation and NAD(P)H oxidation

In previous studies, we observed that aspirin, a promising cancer-preventive agent, induces apoptosis in mitochondrial manganese superoxide dismutase (MnSOD)-deficient Saccharomyces cerevisiae cells grown aerobically in ethanol medium. In this study, we show that aspirin-induced apoptosis is associated with a significant increase in mitochondrial and cytosolic O2 ·- and oxidation of mitochondrial NAD(P)H. A concomitant rise in the level of cytosolic CuZnSOD activity failed to compensate for mitochondrial MnSOD deficiency. However, an observed increase in activity of Escherichia coli FeSOD targeted to the mitochondrial matrix of the MnSOD-deficient yeast cells, markedly decreased aspirin-induced accumulation of mitochondrial O2 ·-, significantly increased the mitochondrial NAD(P)H level and rescued the apoptotic phenotype. Indeed, recombinant yeast cells expressing E. coli FeSOD behaved in a similar manner to the parent wild-type yeast cells with native mitochondrial MnSOD activity. Wild-type cells consistently showed a decrease in mitochondrial O2 ·- and an increase in mitochondrial NAD(P)H levels in the presence of aspirin in ethanol medium. In fact, in wild-type cells, our studies supported an antioxidant action of aspirin. Taken together, our results indicate that a pro-oxidant effect of aspirin occurring predominantly in cells with compromised mitochondrial redox balance may be enough to overcome antioxidant defences resulting in apoptosis, as observed in MnSOD-deficient yeast cells.

The proapoptotic effect of traditional and novel nonsteroidal anti-inflammatory drugs in mammalian and yeast cells

Nonsteroidal anti-inflammatory drugs (NSAIDs) have long been used to treat pain, fever, and inflammation. However, mounting evidence shows that NSAIDs, such as aspirin, have very promising antineoplastic properties. The chemopreventive, antiproliferative behaviour of NSAIDs has been associated with both their inactivation of cyclooxygenases (COX) and their ability to induce apoptosis via pathways that are largely COX-independent. In this review, the various proapoptotic pathways induced by traditional and novel NSAIDs such as phospho-NSAIDs, hydrogen sulfide-releasing NSAIDs and nitric oxide-releasing NSAIDs in mammalian cell lines are discussed, as well as the proapoptotic effects of NSAIDs on budding yeast which retains the hallmarks of mammalian apoptosis. The significance of these mechanisms in terms of the role of NSAIDs in effective cancer prevention is considered.

Aspirin Induces platelet apoptosis

Aspirin is widely used in the treatment of a number of clinical conditions. Although aspirin is being thought to be a relatively "safe" medicine, it also has some side effects, particularly the risk of bleeding which may be severe and lead to death. The mechanisms, however, are not totally understood. It has been reported recently that aspirin induces apoptosis in many cell types. Thus, the aim of the current study is to explore whether aspirin induces platelet apoptosis. The data show that mitochondrial transmembrane potential (ΔΨm) depolarizations and phosphatidylserine (PS) exposures were dose-dependently induced by aspirin in platelets. To further confirm that aspirin incurs platelet apoptosis, caspase-3 activity was measured in platelets, and the result indicated that aspirin induced caspase-3 activation. Furthermore, the mean volume of platelets incubated with aspirin was obviously reduced. Caspase inhibitor z-VAD-fmk inhibited aspirin induced apoptotic platelet shrinkage and ΔΨm depolarization, but had no effect on PS exposure. In addition, platelets incubated with cyclooxygenase inhibitor indomethacin did not incur ΔΨm depolarazation and PS exposure. Taken together, the data indicate that aspirin induces platelet apoptosis via caspase-3 activation.

Interaction of plant cell signaling molecules, salicylic acid and jasmonic acid, with the mitochondria of Helicoverpa armigera

The cotton bollworm, Helicoverpa armigera is a polyphagous pest in Asia, Africa, and the Mediterranean Europe. Salicylic acid (SA) and jasmonic acid (JA) are the cell signaling molecules produced in response to insect attack in plants. The effect of these signaling molecules was investigated on the oxidative phosphorylation and oxidative stress of H. armigera. SA significantly inhibited the state III and state IV respiration, respiratory control index (RCI), respiratory complexes I and II, induced mitochondrial swelling, and cytochrome c release in vitro. Under in vivo conditions, SA induced state IV respiration as well as oxidative stress in time- and dose-dependent manner, and also inhibited the larval growth. In contrast, JA did not affect the mitochondrial respiration and oxidative stress. SA affected the growth and development of H. armigera, in addition to its function as signaling molecules involved in both local defense reactions at feeding sites and the induction of systemic acquired resistance in plants.

The role of mitochondria in yeast programmed cell death

Mammalian apoptosis and yeast programmed cell death (PCD) share a variety of features including reactive oxygen species production, protease activity and a major role played by mitochondria. In view of this, and of the distinctive characteristics differentiating yeast and multicellular organism PCD, the mitochondrial contribution to cell death in the genetically tractable yeast Saccharomyces cerevisiae has been intensively investigated. In this mini-review we report whether and how yeast mitochondrial function and proteins belonging to oxidative phosphorylation, protein trafficking into and out of mitochondria, and mitochondrial dynamics, play a role in PCD. Since in PCD many processes take place over time, emphasis will be placed on an experimental model based on acetic acid-induced PCD (AA-PCD) which has the unique feature of having been investigated as a function of time. As will be described there are at least two AA-PCD pathways each with a multifaceted role played by mitochondrial components, in particular by cytochrome c.

Oxidative stress and programmed cell death in yeast

Yeasts, such as Saccharomyces cerevisiae, have long served as useful models for the study of oxidative stress, an event associated with cell death and severe human pathologies. This review will discuss oxidative stress in yeast, in terms of sources of reactive oxygen species (ROS), their molecular targets, and the metabolic responses elicited by cellular ROS accumulation. Responses of yeast to accumulated ROS include upregulation of antioxidants mediated by complex transcriptional changes, activation of pro-survival pathways such as mitophagy, and programmed cell death (PCD) which, apart from apoptosis, includes pathways such as autophagy and necrosis, a form of cell death long considered accidental and uncoordinated. The role of ROS in yeast aging will also be discussed.

Rapamycin reduces oxidative stress in frataxin-deficient yeast cells

Friedreich ataxia (FRDA) is a common form of ataxia caused by decreased expression of the mitochondrial protein frataxin. Oxidative damage of mitochondria is thought to play a key role in the pathogenesis of the disease. Therefore, a possible therapeutic strategy should be directed to an antioxidant protection against mitochondrial damage. Indeed, treatment of FRDA patients with the antioxidant idebenone has been shown to improve neurological functions. The yeast frataxin knock-out model of the disease shows mitochondrial iron accumulation, iron-sulfur cluster defects and high sensitivity to oxidative stress. By flow cytometry analysis we studied reactive oxygen species (ROS) production of yeast frataxin mutant cells treated with two antioxidants, N-acetyl-L-cysteine and a mitochondrially-targeted analog of vitamin E, confirming that mitochondria are the main site of ROS production in this model. Furthermore we found a significant reduction of ROS production and a decrease in the mitochondrial mass in mutant cells treated with rapamycin, an inhibitor of TOR kinases, most likely due to autophagy of damaged mitochondria.

Subunits Rip1p and Cox9p of the respiratory chain contribute to diclofenac-induced mitochondrial dysfunction

The widely used drug diclofenac can cause serious heart, liver and kidney injury, which may be related to its ability to cause mitochondrial dysfunction. Using Saccharomyces cerevisiae as a model system, we studied the mechanisms of diclofenac toxicity and the role of mitochondria therein. We found that diclofenac reduced cell growth and viability and increased levels of reactive oxygen species (ROS). Strains increasingly relying on respiration for their energy production showed enhanced sensitivity to diclofenac. Furthermore, oxygen consumption was inhibited by diclofenac, suggesting that the drug inhibits respiration. To identify the site of respiratory inhibition, we investigated the effects of deletion of respiratory chain subunits on diclofenac toxicity. Whereas deletion of most subunits had no effect, loss of either Rip1p of complex III or Cox9p of complex IV resulted in enhanced resistance to diclofenac. In these deletion strains, diclofenac did not increase ROS formation as severely as in the wild-type. Our data are consistent with a mechanism of toxicity in which diclofenac inhibits respiration by interfering with Rip1p and Cox9p in the respiratory chain, resulting in ROS production that causes cell death.

The anthracenedione compound bostrycin induces mitochondria-mediated apoptosis in the yeast Saccharomyces cerevisiae

Bostrycin is an anthracenedione with phytotoxic and antibacterial activity that belongs to the large family of quinones. We have isolated bostrycin from the secondary metabolites of a mangrove endophytic fungus, no. 1403, collected from the South China Sea. Using the yeast Saccharomyces cerevisiae as a model, we show that bostrycin inhibits cell proliferation by blocking the cell cycle at G1 phase and ultimately leads to cell death in a time- and dose-dependent manner. Bostrycin-induced lethal cytotoxicity is accompanied with increased levels of intracellular reactive oxygen species and hallmarks of apoptosis such as chromatin condensation, DNA fragmentation and externalization of phosphatidylserine. We further show that bostrycin decreases mitochondrial membrane electric potential and causes mitochondrial destruction during the progression of cell death. Bostrycin-induced cell death was promoted in YCA1 null yeast strain but was partially rescued in AIF1 null mutant both in fermentative and respiratory media, strongly indicating that bostrycin induces apoptosis in yeast cells through a mitochondria-mediated but caspase-independent pathway.