An endogenous calcium-dependent, caspase-independent intranuclear degradation pathway in thymocyte nuclei: antagonism by physiological concentrations of K(+) ions

A Naturally Derived Watercress Flower-Based Phenethyl Isothiocyanate-Enriched Extract Induces the Activation of Intrinsic Apoptosis via Subcellular Ultrastructural and Ca2+ Efflux Alterations in an In Vitro Model of Human Malignant Melanoma

The aim of the current study was to (i) extract isolated fractions of watercress flowers enriched in polyphenols, phenethyl isothiocyanate and glucosinolates and (ii) characterize the anticancer mode of action of non-lethal, sub-lethal and lethal concentrations of the most potent extract fraction in primary (A375) and metastatic (COLO-679) melanoma cells as well as non-tumorigenic immortalized keratinocyte (HaCaT) cells. Cytotoxicity was assessed via the Alamar Blue assay, whereas ultrastructural alterations in mitochondria and the endoplasmic reticulum were determined via transmission electron microscopy. Mitochondrial membrane depolarization was determined using Mito-MP dye, whereas apoptosis was evaluated through the activation of caspases-3, -8 and -9. Among all extract fractions, the phenethyl isothiocyanate-enriched one (PhEF) possessed significant cytotoxicity against A375 and COLO-679 cells, while HaCaT cells remained relatively resistant at sub-lethal and lethal concentrations. Additionally, ultrastructural subcellular alterations associated with apoptosis were observed by means of increased mitochondrial area and perimeter, decreased cristae density and a shorter distance of the endoplasmic reticulum to the mitochondria, all taking place during "early" time points (2-4 h) of exposure. Moreover, PhEF induced mitochondrial membrane depolarization associated with "late" time points (24 h) of exposure, thereby leading to the activation of intrinsic apoptosis. Finally, the inhibition of cytosolic Ca2+ efflux reduced levels of caspases-9 and -3 activity, suggesting the involvement of Ca2+ efflux in modulating the activation of intrinsic apoptosis. To conclude, our data demonstrate an association of "early" ultrastructural alterations in mitochondria and the endoplasmic reticulum with the "late" induction of intrinsic apoptosis via the modulation of Ca2+ efflux.

VEGF121 Mediates Post-Hypoxia Cardioprotective Effects Via CaSR and Mitochondria-Dependent Protease Pathway

BACKGROUND

Cardiovascular disease is the major cause of death worldwide. Hypoxia-mediated apoptosis in cardiomyocytes is a major cause of cardiovascular disorders. Treatment with vascular endothelial growth factor (VEGF) protein has been tested but operational difficulties have limited its use. However, with the advancements of gene therapy, interest has risen in VEGF-based gene therapy in cardiovascular disorders. However, the precise mechanism by which VEGF replenishment rescues post-hypoxia damage in cardiomyocytes is not known.

OBJECTIVES

To investigate the effect of post-hypoxia VEGF121 expression using neonatal rat cardiomyocytes.

METHODS

Cardiomyocytes isolated from neonatal rats were used to establish an in vitro model of hypoxia-induced cardiac injury. The effect of VEGF overexpression, alone or in combination with small-molecule inhibitors targeting calcium channel, calcium sensitive receptors (CaSR), and calpain on cell growth and proliferation on hypoxia-induced cardiomyocyte injury were determined using an MTT assay, TUNEL staining, Annexin V/PI staining, lactate dehydrogenase and caspase activity. For statistical analysis, a value of P<0.05 was considered to be significant.

RESULTS

The effect of VEGF121 was found to be mediated by CaSR and calpain but was not dependent on calcium channels.

CONCLUSIONS

Our findings, even though using an in vitro setting, lay the foundation for future validation and pre-clinical testing of VEGF-based gene therapy in cardiovascular diseases.

Going beyond nutrition: regulation of potassium homoeostasis as a common denominator of plant adaptive responses to environment

Partially and fully completed plant genome sequencing projects in both lower and higher plants allow drawing a comprehensive picture of the molecular and structural diversities of plant potassium transporter genes and their encoded proteins. While the early focus of the research in this field was aimed on the structure-function studies and understanding of the molecular mechanisms underlying K(+) transport, availability of Arabidopsis thaliana mutant collections in combination with micro-array techniques have significantly advanced our understanding of K(+) channel physiology, providing novel insights into the transcriptional regulation of potassium homeostasis in plants. More recently, posttranslational regulation of potassium transport systems has moved into the center stage of potassium transport research. The current review is focused on the most exciting developments in this field. By summarizing recent work on potassium transporter regulation we show that potassium transport in general, and potassium channels in particular, represent important targets and are mediators of the cellular responses during different developmental stages in a plant's life cycle. We show that regulation of intracellular K(+) homeostasis is essential to mediate plant adaptive responses to a broad range of abiotic and biotic stresses including drought, salinity, and oxidative stress. We further link post-translational regulation of K(+) channels with programmed cell death and show that K(+) plays a critical role in controlling the latter process. Thus, is appears that K(+) is not just the essential nutrient required to support optimal plant growth and yield but is also an important signaling agent mediating a wide range of plant adaptive responses to environment.

Similar to spironolactone, oxymatrine is protective in aldosterone-induced cardiomyocyte injury via inhibition of calpain and apoptosis-inducing factor signaling

Accumulating evidence indicates that oxymatrine (OMT) possesses variously pharmacological properties, especially on the cardiovascular system. We previously demonstrated that activated calpain/apoptosis-inducing factor (AIF)-mediated pathway was the key molecular mechanism in aldosterone (ALD) induces cardiomyocytes apoptosis. In the present study, we extended the experimentation by investigating the effect of OMT on cardiomyocytes exposed to ALD, as compared to spironolactone (Spiro), a classical ALD receptor antagonist. Cardiomyocytes were pre-incubated with OMT, Spiro or vehicle for 1 h, and then, cardiomyocytes were exposed to ALD 24 h. The cell injury was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and lactate dehydrogenase (LDH) leakage ratio. Apoptosis was determined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL) assay, annexin V/PI staining, and relative caspase-3 activity assay. Furthermore, expression of pro-apoptotic proteins including truncated Bid (tBid), calpain and AIF were evaluated by western blot analysis. ALD stimulation increased cardiomyocytes apoptosis, caspase-3 activity and protein expression of calpain, tBid and AIF in the cytosol (p<0.05). Pre-incubated with cardiomyocytes injury and increased caspase-3 activity were significantly attenuated (p<0.05). Furthermore, OMT suppressed ALD-induced high expression of calpain and AIF. And these effects of OMT could be comparable to Spiro. These findings indicated that OMT might be a potential cardioprotective-agent against excessive ALD-induced cardiotoxicity, at least in part, mediated through inhibition of calpain/AIF signaling.

Role of ion transport in control of apoptotic cell death

Cell shrinkage is a hallmark and contributes to signaling of apoptosis. Apoptotic cell shrinkage requires ion transport across the cell membrane involving K(+) channels, Cl(-) or anion channels, Na(+)/H(+) exchange, Na(+),K(+),Cl(-) cotransport, and Na(+)/K(+)ATPase. Activation of K(+) channels fosters K(+) exit with decrease of cytosolic K(+) concentration, activation of anion channels triggers exit of Cl(-), organic osmolytes, and HCO3(-). Cellular loss of K(+) and organic osmolytes as well as cytosolic acidification favor apoptosis. Ca(2+) entry through Ca(2+)-permeable cation channels may result in apoptosis by affecting mitochondrial integrity, stimulating proteinases, inducing cell shrinkage due to activation of Ca(2+)-sensitive K(+) channels, and triggering cell-membrane scrambling. Signaling involved in the modification of cell-volume regulatory ion transport during apoptosis include mitogen-activated kinases p38, JNK, ERK1/2, MEKK1, MKK4, the small G proteins Cdc42, and/or Rac and the transcription factor p53. Osmosensing involves integrin receptors, focal adhesion kinases, and tyrosine kinase receptors. Hyperosmotic shock leads to vesicular acidification followed by activation of acid sphingomyelinase, ceramide formation, release of reactive oxygen species, activation of the tyrosine kinase Yes with subsequent stimulation of CD95 trafficking to the cell membrane. Apoptosis is counteracted by mechanisms involved in regulatory volume increase (RVI), by organic osmolytes, by focal adhesion kinase, and by heat-shock proteins. Clearly, our knowledge on the interplay between cell-volume regulatory mechanisms and suicidal cell death is still far from complete and substantial additional experimental effort is needed to elucidate the role of cell-volume regulatory mechanisms in suicidal cell death.

Phosphatidylserine-mediated cellular signaling

Phosphatidylserine (PS), a phospholipid with a negatively charged head group, is an important constituent of eukaryotic membranes. Rather than being a passive component of cellular membranes, PS plays an important role in a number of signaling pathways. Signaling is mediated by proteins that are recruited and/or activated by PS in one of two ways: via domains that stereospecifically recognize the head group, or by electrostatic interactions with membranes that are rich in PS and therefore display negative surface charge. Such interactions are key to both intracellular and extracellular signaling cascades. PS, exposed extracellularly, is instrumental in triggering blood clotting and also serves as an "eat me" signal for the clearance of apoptotic cells. Inside the cell, a number of pathways depend of PS; these include kinases, small GTPases and fusogenic proteins. This review will discuss the generation and distribution of PS, current methods of phospholipid visualization within live cells, as well as the current understanding of the role of PS in both extracellular and intracellular signaling events.

A unifying mechanism for cancer cell death through ion channel activation by HAMLET

Ion channels and ion fluxes control many aspects of tissue homeostasis. During oncogenic transformation, critical ion channel functions may be perturbed but conserved tumor specific ion fluxes remain to be defined. Here we used the tumoricidal protein-lipid complex HAMLET as a probe to identify ion fluxes involved in tumor cell death. We show that HAMLET activates a non-selective cation current, which reached a magnitude of 2.74±0.88 nA within 1.43±0.13 min from HAMLET application. Rapid ion fluxes were essential for HAMLET-induced carcinoma cell death as inhibitors (amiloride, BaCl₂), preventing the changes in free cellular Na⁺ and K⁺ concentrations also prevented essential steps accompanying carcinoma cell death, including changes in morphology, uptake, global transcription, and MAP kinase activation. Through global transcriptional analysis and phosphorylation arrays, a strong ion flux dependent p38 MAPK response was detected and inhibition of p38 signaling delayed HAMLET-induced death. Healthy, differentiated cells were resistant to HAMLET challenge, which was accompanied by innate immunity rather than p38-activation. The results suggest, for the first time, a unifying mechanism for the initiation of HAMLET’s broad and rapid lethal effect on tumor cells. These findings are particularly significant in view of HAMLET’s documented therapeutic efficacy in human studies and animal models. The results also suggest that HAMLET offers a two-tiered therapeutic approach, killing cancer cells while stimulating an innate immune response in surrounding healthy tissues.

Activation of an apoptotic signal transduction pathway involved in the upregulation of calpain and apoptosis-inducing factor in aldosterone-induced primary cultured cardiomyocytes

In this study, aldosterone (ALD)-induced apoptosis of cardiomyocyte was evaluated based on the previous studies, and the roles of calpain signaling were clarified. Primary cultured rat cardiomyocytes were injured by ALD (0.01-10 μM) for varying time periods. Then, the effects of ethylene glycol tetraacetic acid (EGTA) (0.5 mM), calpeptin (2.5 μM), and spironoclactone (10 μM) were evaluated on cardiomyocytes activated by ALD. Cardiomyocytes that were injured by ALD were assayed by the MTT and LDH leakage ratio. Apoptosis was evaluated by a TUNEL assay, annexin V/PI staining, and caspase-3 activity. The expression of cleavage of Bid (tBid), calpain and apoptosis-inducing factor (AIF) was evaluated by western blot analysis. ALD increased calpain expression and caspase-3 activity and promoted Bid cleavage. It also induced the release of AIF from mitochondria into the cytosol. The upregulation of calpain, tBid and caspase-3 activity were further inhibited by treatment with EGTA in the presence of ALD. Additionally, AIF levels in the cytosol decreased due to EGTA but not due to calpeptin. This was also accompanied by a significant decrease in apoptosis. Furthermore, treatment with spironoclactone not only attenuated the pro-apoptotic effect of ALD but reversed the ALD-induced increase of calpain and AIF levels.

Life and death of lymphocytes: a volume regulation affair

The loss of cell volume, termed apoptotic volume decrease (AVD) has been a hallmark feature of apoptosis. However the role of this characteristic attribute of programmed cell death has always been questioned as to whether it plays an active or passive factor during apoptosis. Here we review studies that suggest that AVD plays an active role during apoptosis and the underlying flux of ions that results in this morphological event regulates the programmed cell death process.

Arabidopsis root K+-efflux conductance activated by hydroxyl radicals: single-channel properties, genetic basis and involvement in stress-induced cell death

Reactive oxygen species (ROS) are central to plant stress response, signalling, development and a multitude of other processes. In this study, the plasma-membrane hydroxyl radical (HR)-activated K(+) channel responsible for K(+) efflux from root cells during stress accompanied by ROS generation is characterised. The channel showed 16-pS unitary conductance and was sensitive to Ca(2+), tetraethylammonium, Ba(2+), Cs(+) and free-radical scavengers. The channel was not found in the gork1-1 mutant, which lacks a major plasma-membrane outwardly rectifying K(+) channel. In intact Arabidopsis roots, both HRs and stress induced a dramatic K(+) efflux that was much smaller in gork1-1 plants. Tests with electron paramagnetic resonance spectroscopy showed that NaCl can stimulate HR generation in roots and this might lead to K(+)-channel activation. In animals, activation of K(+)-efflux channels by HRs can trigger programmed cell death (PCD). PCD symptoms in Arabidopsis roots developed much more slowly in gork1-1 and wild-type plants treated with K(+)-channel blockers or HR scavengers. Therefore, similar to animal counterparts, plant HR-activated K(+) channels are also involved in PCD. Overall, this study provides new insight into the regulation of plant cation transport by ROS and demonstrates possible physiological properties of plant HR-activated K(+) channels.

Reciprocal epigenetic modification of histone H2B occurs in chromatin during apoptosis in vitro and in vivo

Histone H2B phosphorylation at Serine 14 (phosS14) has been proposed as an epigenetic marker of apoptotic cells whereas acetylation at the adjacent Lysine 15 (acK15) is a property of non-dying cells. We investigated the relationship and the potential regulatory mechanisms between these two epigenetic histone modifications and internucleosomal DNA degradation during apoptosis. Using rat primary thymocytes induced to undergo apoptosis with glucocorticoids we found that H2B phosphorylated at Ser14 was associated with soluble, cleaved DNA in apoptotic nuclei. In contrast acK15 was prevalent in non-apoptotic nuclei and scarce in apoptotic nuclei. This switch between K15 acetylation and S14 phosphorylation on H2B was also observed in apoptotic thymocytes from animals treated in vivo with glucocorticoids and in a rat hepatoma cell line (HTC) induced to die by UV-C or Fas ligand. Interestingly the combined use of a histone deacetylase inhibitor and glucocorticoid suppressed both S14 phosphorylation and internucleosomal DNA degradation without inhibiting apoptosis in thymocytes. Using synthetic peptides and a PKC phosphorylation assay system, we show that the deacetylation of K15 was necessary to allow the S14 phosphorylation. These findings suggest that selective chromatin post-translational modifications are associated with DNA degradation during apoptosis.

Intracellular DNA release and elimination correlate poorly with transgene expression after non-viral transfection

The intracellular limiting steps in non-viral gene delivery are still unclear. The purpose of this study was to quantize intracellular DNA release and elimination kinetics after transfection with various non-viral carriers (calcium phosphate precipitates, branched poly(ethyleneimine), poly-L-lysine, DOTAP, DOTAP/DOPE) and to correlate these factors with transgene expression. Intracellular kinetics of DNA was determined by novel quantitative method based on qRT-PCR and DNase treatment. Intracellular elimination of DNA after calcium phosphate transfection was rapid (half-life of 0.37 h) whereas the amount of DNA in the cells was stable for at least 136 h after poly(ethyleneimine) mediated transfection. Intracellular elimination half-lives for DNA delivered by other carrier systems ranged from 9 to 27 h. Calcium phosphate precipitates are not able to protect DNA, which explains the short elimination half-life. In the case of other carriers DNA is after complex removal mostly carrier bound but after 24 h the major fraction of DNA is in the released or loosened state. Overall, neither total nor released amount of intracellular DNA correlates with the transgene expression.