Signal transduction pathways in apoptosis

Papaverine provides neuroprotection by suppressing neuroinflammation and apoptosis in the traumatic brain injury via RAGE- NF-<kappa>B pathway

The receptor for advanced glycation end products (RAGE)- Nuclear Factor kappa B (NF-κB) signal pathway may represent a new target for the treatment of traumatic brain injury (TBI). The aim of the study is to investigate effects of papaverine on secondary signaling mechanisms through this pathway in mice TBI model.Immunohistochemically, while the number of RAGE and NF- κB positive cells, apoptotic cells increased, the number of NeuN positive cells reduced in TBI.Papaverine reduced the number of RAGE positive cells on glia and the number of NF- κB positive cells on both neuron and glia. At the same time, it decreased the number of microglia labeled with P2RY12 increased due to TBI. It also increased the NeuN positive cells and mitigated the brain edema. Results of this study showed that papaverine reduced TBI- induced neuroinflammation and apoptosis, also provided neuroprotection via the RAGE- NF-κB signal path, which is one of the possible mechanisms in TBI.

What is pH regulation, and why do cancer cells need it?

Metabolism is a continuous source of acids. To keep up with a desired metabolic rate, tumors must establish an adequate means of clearing their acidic end-products. This homeostatic priority is achieved by various buffers, enzymes, and transporters connected through the common denominator of H⁺ ions. Whilst this complexity is proportionate to the importance of adequate pH control, it is problematic for developing an intuition for tracking the route taken by acids, assessing the relative importance of various acid-handling proteins, and predicting the outcomes of pharmacological inhibition or genetic alteration. Here, with the help of a simplified mathematical framework, the genesis of cancer pH regulation is explained in terms of the obstacles to efficient acid venting and how these are overcome by specific molecules, often associated with cancer. Ultimately, the pH regulatory apparatus in tumors must (i) provide adequate lactic acid permeability through membranes, (ii) facilitate CO₂/HCO₃⁻/H⁺ diffusivity across the interstitium, (iii) invest in a form of active transport that strikes a favorable balance between intracellular pH and intracellular lactate retention under the energetic constraints of a cell, and (iv) enable the necessary feedback to complete the homeostatic loop. A more informed and quantitative approach to understanding acid-handling in cancer is mandatory for identifying vulnerabilities, which could be exploited as therapeutic targets.

Protective effects of trehalose on frozen-thawed ovarian granulosa cells of cattle

In this study, trehalose was investigated for its cryoprotective effects on ovarian granulosa cells (bGCs) of cattle. Five concentrations of trehalose at 0, 0.2, 0.4, 0.6 and 0.8 mol/L were added to the cryopreservation medium of bGCs, and the effects on the quality of frozen-thawed bGCs were assessed. The results indicate that the use of cryopreservation medium containing 0.2 and 0.4 mol/L of trehalose resulted in a greater rate of bGC viability compared to those of other groups (P<0.05). Culturing with trehalose at 0.2 and 0.4 mol/L increased 17β- estradiol (E₂)and decreased progesterone (P₄)production (P < 0.05) in post-thawed bGCs. Compared with the control group, the intracellular Ca²⁺ concentrations of frozen-thawed bGCs were less in all treatment groups (P<0.05), and the least Ca²⁺ concentration was observed in the group containing 0.4 mol/L trehalose. The plasma membrane potentials of frozen-thawed bGCs were greater in the groups with 0.2 and 0.4 mol/L trehalose, and the group treated with 0.4 mol/L trehalose had the greatest membrane potential in comparison to other groups (P < 0.05). The relative abundance of the CYP19 mRNA in frozen-thawed bGCs was greater in the groups containing 0.2, 0.4 and 0.6 mol/L trehalose, and relative abundances of FSHR and BCL2 mRNA were greater in the group of bGCs treated with 0.2 mol/L trehalose (P<0.05). Trehalose treatment at 0.4, 0.6 and 0.8 mol/L had an inhibitory effect on BAX gene transcription in frozen-thawed bGCs (P<0.05). In summary, trehalose exhibited a greater cryoprotective effect on bGCs than basic cryopreservation medium.

Vernodalol mediates antitumor effects in acute promyelocytic leukemia cells

Acute promyelocytic leukemia (APL) remains a challenge to cure due to the side effects of cytotoxic chemotherapy and drug resistance. The present study demonstrated that vernodalol, an active compound isolated from Centratherum anthelminticum, suppresses APL cell proliferation and induces cell cycle arrest in the G2/M phase through the upregulation of p21 and cell division cycle 25. In addition, vernodalol induced cellular apoptosis via the mitochondrial pathway as observed by the cleavage of caspase-9 as well as the release of cytochrome c and Smac/DIABLO into the cytosol. A mechanistic study revealed that vernodalol may exert its antitumor activity through the suppression of phosphoinositide 3-kinase/protein kinase B/mechanistic target of rapamycin signaling. In conclusion, vernodalol may be developed as a potential therapeutic compound for the treatment of APL.

Role of extracellular calcium and mitochondrial oxygen species in psychosine-induced oligodendrocyte cell death

Globoid cell leukodystrophy (GLD) is a metabolic disease caused by mutations in the galactocerebrosidase (GALC) gene. GALC is a lysosomal enzyme whose function is to degrade galacto-lipids, including galactosyl-ceramide and galactosyl-sphingosine (psychosine, PSY). GALC loss of function causes progressive intracellular accumulation of PSY. It is widely held that PSY is the main trigger for the degeneration of myelinating cells and progressive white-matter loss. However, still little is known about the molecular mechanisms by which PSY imparts toxicity. Here, we address the role of calcium dynamics during PSY-induced cell death. Using the human oligodendrocyte cell line MO3.13, we report that cell death by PSY is accompanied by robust cytosolic and mitochondrial calcium (Ca(2+)) elevations, and by mitochondrial reactive oxygen species (ROS) production. Importantly, we demonstrate that the reduction of extracellular calcium content by the chelating agent ethylenediaminetetraacetic acid can decrease intra-mitochondrial ROS production and enhance cell viability. Antioxidant administration also reduces mitochondrial ROS production and cell loss, but this treatment does not synergize with Ca(2+) chelation. Our results disclose novel intracellular pathways involved in PSY-induced death that may be exploited for therapeutic purposes to delay GLD onset and/or slow down its progression.

Arsenic sulfide as a potential anti‑cancer drug

Arsenic sulfide (As4S4) is the main component of realgar, which is widely used in traditional Chinese medicine. Previous studies have shown the beneficial effects of As4S4 in the treatment of hematological malignant diseases, however, its effects on solid tumors have yet to be fully elucidated. The current study aimed to explore the anti‑cancer effect and the mechanism of As4S4 on solid tumors in vitro and in vivo. Cells from four human solid tumor cell lines, including the MKN45 gastric cancer cell line, the A375 malignant melanoma cell line, the 8898 pancreatic carcinoma cell line and the HepG2 hepatocellular carcinoma cell line, were treated with As4S4 in vitro, using the L02 embryonic liver cells as a control. The efficacy of As4S4 was assessed in vivo using mice implanted with Lewis lung carcinoma cells. The results of the current study demonstrated that As4S4 significantly inhibited the proliferation of solid tumor cells in a dose‑ and time‑dependent manner, but produced a less pronounced effect on L02 cells. Additionally, As4S4 was observed to induce apoptosis (including morphological changes and an enhanced sub‑G1 population), which was accompanied by the activation of caspase‑3 and ‑9. Furthermore, treatment with As4S4 significantly inhibited the growth of implanted tumors in mice. These results suggest that As4S4 possesses potent in vitro and in vivo antitumor activity via the induction of cell apoptosis.

The chemistry, physiology and pathology of pH in cancer

Cell survival is conditional on the maintenance of a favourable acid-base balance (pH). Owing to intensive respiratory CO2 and lactic acid production, cancer cells are exposed continuously to large acid-base fluxes, which would disturb pH if uncorrected. The large cellular reservoir of H(+)-binding sites can buffer pH changes but, on its own, is inadequate to regulate intracellular pH. To stabilize intracellular pH at a favourable level, cells control trans-membrane traffic of H(+)-ions (or their chemical equivalents, e.g. ) using specialized transporter proteins sensitive to pH. In poorly perfused tumours, additional diffusion-reaction mechanisms, involving carbonic anhydrase (CA) enzymes, fine-tune control extracellular pH. The ability of H(+)-ions to change the ionization state of proteins underlies the exquisite pH sensitivity of cellular behaviour, including key processes in cancer formation and metastasis (proliferation, cell cycle, transformation, migration). Elevated metabolism, weakened cell-to-capillary diffusive coupling, and adaptations involving H(+)/H(+)-equivalent transporters and extracellular-facing CAs give cancer cells the means to manipulate micro-environmental acidity, a cancer hallmark. Through genetic instability, the cellular apparatus for regulating and sensing pH is able to adapt to extracellular acidity, driving disease progression. The therapeutic potential of disturbing this sequence by targeting H(+)/H(+)-equivalent transporters, buffering or CAs is being investigated, using monoclonal antibodies and small-molecule inhibitors.

Calcium signalling and the regulation of apoptosis

Apoptotic cell death is characterized by cell shrinkage, chromatin condensation and fragmentation, formation of apoptotic bodies and phagocytosis (Kerr et al., 1972). At the molecular level, activation of a family of cysteine proteases, caspases, related to interleukin-1beta-converting enzyme is believed to be a crucial event in apoptosis. This is associated with the proteolysis of nuclear and cytoskeletal proteins, cell shrinkage, glutathione efflux, exposure of phosphatidylserine on the cell surface, membrane blebbing, etc. In CD95- or TNF-mediated apoptosis, the proteolytic cascade is believed to be triggered directly by caspase binding to the activated plasma membrane receptor complex. In other forms of apoptosis, the mechanisms of activation of the proteolytic cascade are less well established but may involve imported proteases, such as granzyme B, or factors released from the mitochondria and, possibly, other organelles. Recently, the possibility that cytochrome c released from the mitochondria may serve to activate dormant caspases in the cytosol, and thereby to propagate the apoptotic process, has attracted considerable attention. A perturbation of intracellular Ca(2+) homeostasis has been found to trigger apoptosis in many experimental systems, and the apoptotic process has been related to either a sustained increase in cytosolic free Ca(2+) level or a depletion of intracellular Ca(2+) stores. Although many of the biochemical events involved in the apoptotic process are Ca(2+) dependent, the exact mechanism by which Ca(2+) triggers apoptosis remains unknown. The bcl-2 gene family, which includes both inhibitors and inducers of apoptosis, appears to regulate intracellular Ca(2+) compartmentalization. The induction of apoptosis by Ca(2+)-mobilizing agents results in caspase activation, which is similar to what is seen with other inducers of apoptosis. In addition, Ca(2+)-dependent proteases, such as calpain and a Ca(2+)-dependent nuclear scaffold-associated serine protease, are also activated by Ca(2+) signalling in some cell types where they appear to be involved in alpha-fodrin and lamin beta cleavage, respectively. Thus, a spectrum of proteases are activated during apoptosis depending on both cell type and inducer. This proteolytic cascade can involve both caspases and Ca(2+)-dependent proteases, which seem to interact during the apoptotic process.

Cellular signal transduction can be induced by TRAIL conjugated to microcapsules

The extracellular agent tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) can induce apoptosis in tumor cells but spare normal cells. Ligation of TRAIL to a nanoparticle would serve to facilitate targeting to an extravascular site. Polymeric ultrasound contrast agents (UCA) (microencapsulated gas bubbles) can be tracked by ultrasound imaging, and fragmented into nanoparticles by focused ultrasound. This tumor-targeted delivery system has been shown to deliver more efficiently than solid nanoparticles. Additionally, small molecule inhibitors such as bortezomib, shown to sensitize TRAIL-resistant cells, could be co-administered within these UCA. In this pilot study, TRAIL was conjugated to UCA while preserving the agent's sensitivity to ultrasound. Human cancer cell lines, OVCAR-3 and A2058, were bathed with the TRAIL-UCA with and without the addition of bortezomib. Apoptosis was quantified using flow cytometry. OVCAR-3 treated with TRAIL-UCA exhibit significant (p < 0.05) apoptotosis compared to unmodified UCA, equal to positive controls, but no synergistic effect when combined with bortezomib. A2058 cells treated with TRAIL-UCA also exhibited significant apoptosis (p < 0.01) compared to unmodified UCA, similar to positive controls and bortezomib significantly increased apoptosis in combination with TRAIL-UCA. We conclude that TRAIL-ligated UCA show exciting potential as a new therapy.

Pulse modulated 900 MHz radiation induces hypothyroidism and apoptosis in thyroid cells: a light, electron microscopy and immunohistochemical study

PURPOSE

In the present study we investigated the possible histopathological effects of pulse modulated Radiofrequency (RF) fields on the thyroid gland using light microscopy, electron microscopy and immunohistochemical methods.

MATERIALS AND METHODS

Two months old male Wistar rats were exposed to a 900 MHz pulse-modulated RF radiation at a specific absorption rate (SAR) of 1.35 Watt/kg for 20 min/day for three weeks. The RF signals were pulse modulated by rectangular pulses with a repetition frequency of 217 Hz and a duty cycle of 1:8 (pulse width 0.576 ms). To assess thyroid endocrine disruption and estimate the degree of the pathology of the gland, we analysed structural alterations in follicular and colloidal diameters and areas, colloid content of the follicles, and height of the follicular epithelium. Apoptosis was confirmed by Transmission Electron Microscopy and assessing the activites of an initiator (caspase-9) and an effector (caspase-3) caspases that are important markers of cells undergoing apoptosis.

RESULTS

Morphological analyses revealed hypothyrophy of the gland in the 900 MHz RF exposure group. The results indicated that thyroid hormone secretion was inhibited by the RF radiation. In addition, we also observed formation of apoptotic bodies and increased caspase-3 and caspase-9 activities in thyroid cells of the rats that were exposed to modulated RF fields.

CONCLUSION

The overall findings indicated that whole body exposure to pulse-modulated RF radiation that is similar to that emitted by global system for mobile communications (GSM) mobile phones can cause pathological changes in the thyroid gland by altering the gland structure and enhancing caspase-dependent pathways of apoptosis.

Apoptogenic effect of 7,8-diacetoxy-4-methylcoumarin and 7,8-diacetoxy-4-methylthiocoumarin in human lung adenocarcinoma cell line: role of NF-kappaB, Akt, ROS and MAP kinase pathway

Coumarin (1,2-benzopyrone) is a naturally occurring fragrant compound found in a variety of plants and spices. Coumarins have attracted intense interest in recent years because of their diverse pharmacological activities. This study examines the antioxidant coumarin 7,8-diacetoxy-4-methylcoumarin (DAMC) and its thiocoumarin derivative 7,8-diacetoxy-4-methylthiocoumarin (DAMTC) for their effect on human non-small cell lung cancer A549 cells. Here we show that both DAMC and DAMTC not only inhibited cell proliferation, but also induced apoptosis with an IC(50) of 160 microg/ml as confirmed by morphological examination, annexin-V assay and flow cytometric analysis. Interestingly, it was observed that these two coumarin compounds exhibited little cytotoxicity towards peripheral blood mononuclear cells but induced apoptosis in malignant cells. DAMC/DAMTC treatment also resulted in pronounced release of apoptogenic cytochrome c from mitochondria to cytosol, alteration of mitochondrial membrane potential (DeltaPsi(m)), and activation of caspase-9 and caspase-3. Although an increase in the levels of reactive oxygen species (ROS) was observed, pre-treatment with antioxidant showed no protective effect against DAMC/DAMTC-induced apoptosis. Results of present study suggest that downregulation of Bcl-xl, Cox-2 and mitogen activated protein kinase pathway and upregulation of p53, Akt and NF-kappaB pathway are involved in the underlying molecular mechanism of apoptosis induction by DAMC and DAMTC in A549 cells.

Loss of homeostatic tension induces apoptosis in tendon cells: an in vitro study

Apoptosis (programmed cell death) has been identified as a histopathologic feature of tendinopathy. While the precise mechanism(s) that triggers the apoptotic cascade in tendon cells has not been identified, it has been theorized that loss of cellular homeostatic tension following microscopic damage to individual tendon fibrils could be the stimulus for initiating the pathologic events associated with tendinopathy. To determine if loss of homeostatic tension following stress deprivation could induce apoptosis in tendon cells, rat tail tendons were stress-deprived or cyclically loaded (3% strain at 0.17 Hz) for 24 hours under tissue culture conditions. Caspase-3 (an upstream mediator of apoptosis) mRNA expression was evaluated using quantitative polymerase chain reaction and caspase-3 protein synthesis was identified using immunohistochemistry. Apoptotic cells were identified histologically using an antibody for single-stranded DNA. Stress deprivation for 24 hours resulted in an increase in caspase-3 mRNA expression when compared to fresh controls or cyclically loaded tendons. Stress deprivation also increased the percentage of apoptotic cells (10.59% +/- 2.80) compared to controls (1.87% +/- 1.07) or cyclically loaded tendons (3.73% +/- 0.87). These data suggest loss of homeostatic tension following stress deprivation induces apoptosis in rat tail tendon cells.

Platelet-activating factor-induced chloride channel activation is associated with intracellular acidosis and apoptosis of intestinal epithelial cells

Platelet-activating factor (PAF) is a phospholipid inter- and intracellular mediator implicated in intestinal injury primarily via induction of an inflammatory cascade. We find that PAF also has direct pathological effects on intestinal epithelial cells (IEC). PAF induces Cl(-) channel activation, which is associated with intracellular acidosis and apoptosis. Using the rat small IEC line IEC-6, electrophysiological experiments demonstrated that PAF induces Cl(-) channel activation. This PAF-activated Cl(-) current was inhibited by Ca(2+) chelation and a calcium calmodulin kinase II inhibitor, suggesting PAF activation of a Ca(2+)-activated Cl(-) channel. To determine the pathological consequences of Cl(-) channel activation, microfluorimetry experiments were performed, which revealed PAF-induced intracellular acidosis, which is also inhibited by the Cl(-) channel inhibitor 4,4'diisothiocyanostilbene-2,2'disulfonic acid and Ca(2+) chelation. PAF-induced intracellular acidosis is associated with caspase 3 activation and DNA fragmentation. PAF-induced caspase activation was abolished in cells transfected with a pH compensatory Na/H exchanger construct to enhance H(+) extruding ability and prevent intracellular acidosis. As ClC-3 is a known intestinal Cl(-) channel dependent on both Ca(2+) and calcium calmodulin kinase II phosphorylation, we generated ClC-3 knockdown cells using short hairpin RNA. PAF induced Cl(-) current; acidosis and apoptosis were all significantly decreased in ClC-3 knockdown cells. Our data suggest a novel mechanism of PAF-induced injury by which PAF induces intracellular acidosis via activation of the Ca(2+)-dependent Cl(-) channel ClC-3, resulting in apoptosis of IEC.

Regulation of tumor pH and the role of carbonic anhydrase 9

The high metabolic rate required for tumor growth often leads to hypoxia in poorly-perfused regions. Hypoxia activates a complex gene expression program, mediated by hypoxia inducible factor 1 (HIF1alpha). One of the consequences of HIF1alpha activation is up-regulation of glycolysis and hence the production of lactic acid. In addition to the lactic acid-output, intracellular titration of acid with bicarbonate and the engagement of the pentose phosphate shunt release CO(2) from cells. Expression of the enzyme carbonic anhydrase 9 on the tumor cell surface catalyses the extracellular trapping of acid by hydrating cell-generated CO(2) into [see text] and H(+). These mechanisms contribute towards an acidic extracellular milieu favoring tumor growth, invasion and development. The lactic acid released by tumor cells is further metabolized by the tumor stroma. Low extracellular pH may adversely affect the intracellular milieu, possibly triggering apoptosis. Therefore, primary and secondary active transporters operate in the tumor cell membrane to protect the cytosol from acidosis. We review mechanisms regulating tumor intracellular and extracellular pH, with a focus on carbonic anhydrase 9. We also review recent evidence that may suggest a role for CA9 in coordinating pH(i) among cells of large, unvascularized cell-clusters.

Is digitalis compound-induced cardiotoxicity, mediated through guinea-pig cardiomyocytes apoptosis?

Our aim in performing this study was to analyze in vivo the cell death mechanism induced by toxic doses of digitalis compounds on guinea-pig cardiomyocytes. We analyzed three study groups of five male guinea pigs each. Guinea pigs were intoxicated under anesthesia with ouabain or digoxin (at a 50-60% lethal dose); the control group did not receive digitalis. A 5-hours period elapsed before guinea pig hearts were extracted to obtain left ventricle tissue. We carried out isolation of mitochondria and cytosol, cytochrome c and caspase-3 and -9 determination, and electrophoretic analysis of nuclear DNA. TdT-mediated DUTP-X nick end labeling (TUNEL) reaction was performed in histologic preparations to identify in situ apoptotic cell death. Ultrastructural analysis was performed by electron microscopy. Electrophoretic analysis of DNA showed degradation into fragments of 200-400 base pairs in digitalis-treated groups. TUNEL reaction demonstrated the following: in the control group, <10 positive nuclei per field; in the digoxin-treated group, 2-14 positive nuclei per field, while in the ouabain-treated group counts ranged from 9-30 positive nuclei per field. Extracts from ouabain-treated hearts had an elevation of cytochrome c in cytosol and a corresponding decrease in mitochondria; this release of cytochrome c provoked activation of caspase-9 and -3. Electron microscopy revealed presence of autophagic vesicles in cytoplasm of treated hearts. Toxic dosages of digitalis at 50-60% of the lethal dose are capable of inducing cytochrome c release from mitochondria, processing of procaspase-9 and -3, and DNA fragmentation; these observations are mainly indicative of apoptosis, although a mixed mechanism of cell death cannot be ruled out.

Reversing drug resistance in bcl-2-expressing tumor cells by depleting glutathione

The immense research effort in cancer cell physiology has led to an appreciation of the molecular and biochemical pathways that regulate cellular responses to endogenous and exogenous insults. Similarly, in tumor cells, there are multiple overlapping pathways that, once activated, impart resistance to therapeutic intervention. The multi drug resistance pathway is one such pathway. In this review, we will present current ideas concerning a mechanism of tumor cell resistance that involves the inability to undergo apoptosis. The bcl-2 family of proteins are known to regulate apoptosis in response to a wide variety of toxic agents. Additionally, recent evidence points to bcl-2 involvement in the regulation of antioxidant pathways mediated by glutathione. This new information will be discussed in some detail and strategies for overcoming these resistance mechanisms that may have clinical utility will be presented.

Capsaicin-induced apoptosis of glioma cells is mediated by TRPV1 vanilloid receptor and requires p38 MAPK activation

We provide evidence on the expression of the transient receptor potential vanilloid type-1 (TRPV1) by glioma cells, and its involvement in capsaicin (CPS)-induced apoptosis. TRPV1 mRNA was identified by quantitative RT-PCR in U373, U87, FC1 and FLS glioma cells, with U373 cells showing higher, and U87, FC1 and FLS cells lower TRPV1 expression as compared with normal human astrocytes. By flow cytometry we found that a substantial portion of both normal human astrocytes, and U87 and U373 glioma cells express TRPV1 protein. Moreover, we analyzed the expression of TRPV1 at mRNA and protein levels of glioma tissues with different grades. We found that TRPV1 gene and protein expression inversely correlated with glioma grading, with marked loss of TRPV1 expression in the majority of grade IV glioblastoma multiforme. We also described that CPS trigger apoptosis of U373, but not U87 cells. CPS-induced apoptosis involved Ca(2+) influx, p38 but not extracellular signal-regulated mitogen-activated protein kinase activation, phosphatidylserine exposure, mitochondrial permeability transmembrane pore opening and mitochondrial transmembrane potential dissipation, caspase 3 activation and oligonucleosomal DNA fragmentation. TRPV1 was functionally implicated in these events as they were markedly inhibited by the TRPV1 antagonist, capsazepine. Finally, p38 but not extracellular signal-regulated protein kinase activation was required for TRPV1-mediated CPS-induced apoptosis of glioma cells.

The immunomodulatory protein SV-IV protects serum-deprived cells against apoptosis but not against G0/G1 arrest: Possible implications for the survival of implanting embryo

Serum deprivation induced in human lymphoblastoid Raji cells oxidative stress-associated apoptotic death and G0/G1 cell cycle arrest. Addition into culture medium of the immunomodulatory protein Seminal vesicle protein 4 (SV-IV) protected these cells against apoptosis but not against cycle arrest. The antiapoptotic activity was related to: (1) decrease of endocellular reactive Oxygen species (ROS) (2) increase of mRNAs encoding anti-oxidant enzymes (catalase, G6PD) and antiapoptotic proteins (survivin, cox-1, Hsp70, c-Fos); (3) decrease of mRNAs encoding proapoptotic proteins (c-myc, Bax, caspase-3, Apaf-1). The biochemical changes underlaying these effects were probably induced by a protein tyrosine kinase (PTK) activity triggered by the binding of SV-IV to its putative plasma membrane receptors. The ineffectiveness of SV-IV to abrogate the cycle arrest was accounted for by its downregulating effects on D1,3/E G1-cyclins and CdK2/4 gene expression, ppRb/pRb ratio, and intracellular ROS concentration. In conclusion, these experiments: (1) prove that SV-IV acts as a cell survival factor; (2) suggest the involvement of a PTK in SV-IV signaling; (3) point to cell cycle-linked enzyme inhibition as responsible for cycle arrest; (4) provide a model to dissect the cycle arrest and apoptosis induced by serum withdrawal; (5) imply a possible role of SV-IV in the survival of hemiallogenic implanting embryos.

Prostacyclin prevents nitric oxide-induced megakaryocyte apoptosis

1 We have previously demonstrated that nitric oxide (NO) triggers CD34(+)-derived megakaryocyte apoptosis. We here show that prostacyclin (PGI(2)) inhibits PAPA/NO-induced megakaryocyte death detected by fluorescent microscopy and flow cytometry. 2 The cAMP-specific phosphodiesterase inhibitor, Ro 20-1724, and the permeable analog dibutyryl-cAMP also delayed apoptosis. PGI(2) effect was fully prevented when adenylyl cyclase activity was suppressed by SQ 22536, and partially reversed by the permeable protein kinase A inhibitor PKI 14-22 amide. ELISA showed that while both PGI(2) and NO alone or synergistically raised cAMP, only NO was able to increase intracellular cGMP levels. 3 Treatment of megakaryocytes with PGI(2) abolished both basal and NO-raised cGMP levels. Addition of 8-pCPT-cGMP or activation of soluble guanylyl cyclase by BAY 41-2272 induced cell death in a concentration-dependent manner, and ODQ, an inhibitor of guanylyl cyclase, prevented both PAPA/NO- or BAY 41-2272-induced apoptosis. Specific cGMP phosphodiesterase inhibition by Zaprinast or suppression of adenylyl cyclase by SQ 22536 enhanced the PAPA/NO proapoptotic effect. 4 PGI(2) completely inhibited NO-mediated generation and the increased activity of the cleaved form of caspase-3. 5 In conclusion, our results demonstrate that contrary to their well-known direct and synergistic inhibitory effects on platelets, PGI(2) and NO regulate opposite megakaryocyte survival responses through a delicate balance between intracellular cyclic nucleotide levels and caspase-3 activity control.

The spread of apoptosis through gap-junctional channels in BHK cells transfected with Cx32

Programmed cell death (apoptosis) occurs both during normal development and as a result of various pathological conditions. An in vitro system was used to explore the transmission of death signals from apoptotic cells to cells with which they were coupled via gap junctions. Confluent cultures of baby hamster kidney (BHK) cells, stably transfected with the gap-junctional protein connexin32, were scrape loaded with cytochrome C (cyC), a mitochondria-derived apoptotic agent, to introduce the protein into cells injured by the cut. The cultures were subsequently analyzed for the presence of activated caspases, the distribution of TUNEL staining, and the binding of annexin V. Although cyC is too large to traverse the gap junctional channel, each of the assays revealed that apoptosis had spread from dying cells at the margin of the scrape to otherwise healthy neighboring cells to which they were coupled. This "bystander effect" was significantly reduced in the presence of agents that block gap junctional intercellular communication.

Tumor necrosis factor-α-induced changes in insulin-producing β-cells

The migration of macrophages and lymphocytes that produce cytokines such as tumor necrosis factor-alpha (TNF-alpha) causes beta-cell death, leading to type 1 diabetes. Similarly, in type 2 diabetes, the adipocyte-derived cytokines including TNF-alpha are elevated in the circulation, causing inflammation and insulin resistance. Thus, the studies described in this article using TNF-alpha are relevant to furthering our understanding of the pathogenesis of diabetes mellitus. We used RINr1046-38 (RIN) insulin-producing beta-cells, which constitutively express calbindin-D(28k), to characterize the effect of TNF-alpha on apoptosis, replication, insulin release, and gene and protein expression. Western blots of TNF-alpha-treated RIN cells revealed a decrease in calbindin-D(28k). By ELISA, TNF-alpha-treated beta-cells had 47% less calbindin-D(28k) than controls. In association with the decline in calbindin-D(28k), TNF-alpha treatment of RIN cells led to a 73% greater increase in changes in intracellular calcium concentration (Delta[Ca(2+)](i)) in TNF-alpha-treated cells as compared to that in control RIN cells upon treatment with 50 mM KCl; caused a greater increase in the [Ca(2+)](i) following the addition of 5.5 microM ionomycin; increased by more than threefold the apoptotic rate, expressed as the percentage of TUNEL-positive nuclei to total nuclei; decreased the rate of cell replication by 36%; and increased and decreased selectively the expression of specific genes as determined by microarray analysis. The subcellular localizations of Bcl-2, an antiapoptotic protein, and Bax, a proapoptotic protein, within RIN cells were altered with TNF-alpha treatment such that the two were colocalized with mitochondria in the perinuclear region. We conclude that the proapoptotic action of TNF-alpha on beta-cells is manifested via decreased expression of calbindin-D(28k) and is mediated at least in part by [Ca(2+)](i).

Cyanidin and Malvidin from Oryza sativa cv. Heugjinjubyeo mediate cytotoxicity against human monocytic leukemia cells by arrest of G(2)/M phase and induction of apoptosis

Oryza sativa cv. Heugjinjubyeo (Gramineae), anthocyanin-pigmented rice, having dark purple grains, is known broadly as enriched rice with an improved taste. Two bioactive compounds were isolated from the 0.5% HCl-ethyl alcohol soluble fraction of the aleurone layer of O. sativa cv. Heugjinjubyeo through an activity-monitored fractionation and isolation method. From spectral analysis, the cytotoxic components were the anthocyanidins cyanidin (1) and malvidin (2) The 50% growth inhibitory concentrations (IC(50)) of cyanidin and malvidin on U937, human monocytic leukemia cells, were 60 and 40 microg/mL, respectively. These compounds showed cytotoxicity through the arrest of the G(2)/M phase of cell cycle and induction of apoptosis.

Contributions of protein kinase A anchoring proteins to compartmentation of cAMP signaling in the heart

The cAMP-dependent protein kinase (PKA) transduces signals in the heart initiated by beta(1)-adrenergic, G-protein-coupled receptors after norepinephrine, sympathetic stimulation. Signaling through this pathway results in a characteristic set of cellular responses, including increases in ion fluxes and contractile strength, mobilization of energy stores, and changes in gene expression. Not all receptors that activate adenylate cyclase and increase cAMP levels, however, cause the cardiac myocyte to react in this manner. Research in the field of signal transduction over the last 25 years has addressed this issue of specificity in signaling by diffusable second messengers. PKA is in part targeted to discrete cellular locations by A-kinase anchoring proteins. Through anchoring and formation of multienzyme complexes, specific, localized signal transduction is possible. I discuss in this review recent advances in the understanding of PKA signaling complexes in the cardiac myocyte.

Apoptosis of spinal interneurons induced by sciatic nerve axotomy in the neonatal rat is counteracted by nerve growth factor and ciliary neurotrophic factor

We have previously shown that not only motoneurons and dorsal root ganglion cells but also small neurons, presumably interneurons in the spinal cord, may undergo apoptotic cell death as a result of neonatal peripheral nerve transection in the rat. With the aid of electron microscopy, we have here demonstrated that apoptosis in the spinal cord is confined to neurons and does not involve glial cells at the survival time studied (24 hours). To define the relative importance of the loss of a potential target (motoneuron) and a potential afferent input (dorsal root ganglion cell) for the induction of apoptosis in interneurons in this situation, we have compared the distributions and time courses for TUNEL labeling, which detects apoptotic cell nuclei, in the L5 segment of the spinal cord and the L5 dorsal root ganglion after sciatic nerve transection in the neonatal (P2) rat. In additional experiments, we studied the effects on TUNEL labeling of interneurons after treatment of the cut sciatic nerve with either ciliary neurotrophic factor (CNTF) to rescue motoneurons or nerve growth factor (NGF) to rescue dorsal root ganglion cells. The time courses of the TUNEL labeling in motoneurons and interneurons induced by the lesion show great similarities (peak at 8-48 hours postoperatively), whereas the labeling in dorsal root ganglion cells occurs later (24-72 hours). Both CNTF and NGF decrease the number of TUNEL-labeled interneurons, but there is a regional difference, in that CNTF preferentially saves interneurons in deep dorsal and ventral parts of the spinal cord, whereas the rescuing effects of NGF are seen mainly in the superficial dorsal horn. The results are interpreted as signs of a trophic dependence on both the target and the afferent input for the survival of interneurons neonatally.

Papaverine induces apoptosis in vascular endothelial and smooth muscle cells

Papaverine is a vasodilator commonly used in the treatment of vasospasmic diseases such as cerebral spasm associated with subarachnoid hemorrhage, and in the prevention of spasm of coronary artery bypass graft by intraluminal and/or extraluminal administration. In this study, we examined whether papaverine in the range of concentrations used clinically causes apoptosis of vascular endothelial and smooth muscle cells. Apoptotic cells were identified by morphological changes and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay. In porcine coronary endothelial cells (EC) and rat aortic smooth muscle cells (SMC), papaverine at the concentration of 10(-3) M induced membrane blebbing within 1 hour of incubation. Nuclear condensation and fragmentation were found after 24 hours of treatment. The number of apoptotic cells stained with the TUNEL method was significantly higher in the EC and the SMC after 24 hours of incubation with papaverine at the concentrations of 10(-4) and 10(-3) M than their respective controls. Acidified saline solution (pH 4.8, as control for 10(-3) M papaverine hydrochloride) did not cause apoptosis in these cells. These results showed that papaverine could damage endothelial and smooth muscle cells by inducing changes which are associated with events leading to apoptosis. Since integrity of endothelial cells is critical for normal vascular function, vascular administration of papaverine for clinical use, especially at high concentrations (> or = 10(-4) M), should be re-considered.

ADP-ribose gating of the calcium-permeable LTRPC2 channel revealed by Nudix motif homology

Free ADP-ribose (ADPR), a product of NAD hydrolysis and a breakdown product of the calcium-release second messenger cyclic ADPR (cADPR), has no defined role as an intracellular signalling molecule in vertebrate systems. Here we show that a 350-amino-acid protein (designated NUDT9) and a homologous domain (NUDT9 homology domain) near the carboxy terminus of the LTRPC2/TrpC7 putative cation channel both function as specific ADPR pyrophosphatases. Whole-cell and single-channel analysis of HEK-293 cells expressing LTRPC2 show that LTRPC2 functions as a calcium-permeable cation channel that is specifically gated by free ADPR. The expression of native LTRPC2 transcripts is detectable in many tissues including the U937 monocyte cell line, in which ADPR induces large cation currents (designated IADPR) that closely match those mediated by recombinant LTRPC2. These results indicate that intracellular ADPR regulates calcium entry into cells that express LTRPC2.

Estrogenic upregulation of DNA polymerase beta in oocytes of preovulatory ovine follicles

The basic premise of this investigation was that local hormonal control of stockpiling of the base excision repair polymerase (poly) beta within oocytes of preovulatory follicles occurs as a function of cytoplasmic maturation. There was an increase in immunoreactive poly beta in sectioned oocytes of preovulatory ovine follicles during a 12-36-hour interval following the onset of prostaglandin (PG) F2alpha-induced (Day 14 of the estrous cycle) luteal regression; this response was not observed in subordinate (nonovulatory) follicles. Accumulation of poly beta in oocytes at 36 hr after PGF2alpha was negated by treatment of ewes at 12 hr with the aromatase inhibitor Arimidex or an ovulatory dose of GnRH (which, via surge gonadotropin stimulation, acutely downregulates the proestrous rise in follicular estrogen biosynthesis). Estradiol-17beta stimulated poly beta expression (transcriptional control) in oocytes of explanted (12 hr after PGF2alpha) follicles (24-hour incubation). We suggest that a critical period of estrogen amplification in the preovulatory follicle underscores the capacity of its oocyte to efficiently repair DNA and therefore reconcile spontaneous infidelities in genomic integrity that inevitably occur during preimplantation embryogenesis.

Reactive oxygen species regulate signaling pathways induced by M1 muscarinic receptors in PC12M1 cells

Activation of the m1 muscarinic receptor subtype in rat pheochromocytoma (PC12) cells stably expressing cloned m1 muscarinic acetylcholine receptors was previously shown to induce morphological changes and growth arrest. However, the signaling pathways which lead to these effects were not identified. In an attempt to characterize the intracellular signaling that might be involved in the muscarinic-induced effects, we investigated the role of reactive oxygen species in the regulation of these processes. Stimulation of the muscarinic receptor in these cells increased the intracellular concentrations of reactive oxygen species. Muscarinic activation induced intracellular signaling pathways that involve activation of Ras, extracellular signal-regulated kinase (ERK), and p38. These pathways were partially blocked when reactive oxygen species (ROS) production was prevented by the antioxidant N-acetylcysteine. Other muscarinic-induced signals, such as activation of c-Jun NH(2)-terminal kinase (JNK) or an increase in the binding activity of the transcription factors nuclear factor-kappa B and activator protein-1, were inhibited by the antioxidant dicoumarol. N-Acetylcysteine also blocked the growth arrest and changes in cell shape induced by stimulation of the muscarinic receptor in PC12M1 cells. These findings suggest that ROS act as second messengers in muscarinic-induced cellular signaling. Moreover, generation of ROS appears to be an early and critical intermediary event, which occurs immediately after stimulation of the muscarinic receptor and affects in a variety of mechanisms the muscarinic-mediated cellular signaling.

Anti-apoptotic effect of benidipine, a long-lasting vasodilating calcium antagonist, in ischaemic/reperfused myocardial cells

1. Ischaemia/reperfusion causes intracellular calcium overloading in cardiac cells. Administration of calcium antagonists reduces myocardial infarct size. Recent in vitro studies have demonstrated that calcium plays a critical role in the signal transduction pathway leading to apoptosis. However, whether or not calcium antagonists may reduce myocardial apoptosis induced by ischaemia-reperfusion, and thus decrease myocardial infarction, has not been directly investigated. 2. The present study investigated the effects of benidipine, an L-type calcium channel blocker, on myocardial infarct size, apoptosis, necrosis and cardiac functional recovery in rabbits subjected to myocardial ischaemia/reperfusion (MI/R, 45 min/240 min). Ten minutes prior to coronary occlusion, rabbits were treated with vehicle or benidipine (10 microg x kg(-1) or 3 microg x kg(-1), i.v.). 3. In the vehicle-treated group, MI/R caused cardiomyocyte apoptosis as evidenced by DNA ladder formation and TUNEL positive nuclear staining (12.2+/-1.1%). Treatment with 10 microg x kg(-1) benidipine lowered blood pressure, decreased myocardial apoptosis (6.2+/-0.8%, P<0.01 vs vehicle) and necrosis, reduced infarct size (20+/-2.3% vs 49+/-2.6%, P<0.01), and improved cardiac functional recovery after reperfusion. Administering benidipine at 3 microg x kg(-1), a dose at which no haemodynamic effect was observed, also exerted significant anti-apoptosis effects, which were not significantly different from those observed with higher dose benidipine treatment. However, treatment with this low dose benidipine failed to reduce myocardial necrosis. 4. These results demonstrate that benidipine, a calcium antagonist, exerts significant anti-apoptosis effects, which are independent of haemodynamic changes. Administration of benidipine at a higher dose produced favourable haemodynamic effects and provided additional protection against myocardial necrotic injury and further improved cardiac functional recovery.

Involvement of Intracellular Ca2+in the Regulation of Bovine Leukemia Virus Expression

The calcium ionophore A23187, which was used to increase the intracellular calcium concentration ([Ca2+]i), was analyzed for effects on bovine leukemia virus (BLV) expression in two BLV infected cell lines. To clarify the role of intracellular free calcium in this response, [Ca2+]i was measured during ionophore treatment with the fluorescent calcium indicator Fura-2. Elevation of intracellular calcium under these conditions caused an enhancement of BLV gp51 and p24 synthesis as well as an activation of the BLV long terminal repeat (LTR) in a dose-dependent manner. Furthermore, it was observed that elevated levels of intracellular calcium following A23187 stimulation lead to activation of NF-kappaB. Based on inhibitor studies, we hypothesize that the effect of A23187 on BLV expression appears to be mediated by PKC.

Effects of Mannheimia haemolytica leukotoxin on apoptosis and oncosis of bovine neutrophils

OBJECTIVE

To investigate the concentration-dependent effects of Mannheimia haemolytica (formerly Pasteurella haemolytica) leukotoxin (LKT) on apoptosis and oncosis in bovine neutrophils and to examine the role of calcium ions (Ca2+) in LKT-induced apoptosis.

SAMPLE POPULATION

Neutrophils isolated from blood samples obtained from healthy calves.

PROCEDURE

Neutrophil suspensions were exposed to lytic or sublytic dilutions of LKT and then examined by use of transmission electron microscopy (TEM) or gel electrophoresis. Contribution of extracellular Ca2+ to LKT-induced apoptosis was investigated by incubating neutrophils with LKT or control solutions in buffer containing 1 mM CaCl2 or in Ca2+-free buffer containing 1 mM ethylene glycol-bis (b-aminoethyl ether)-N,N-tetraacetic acid (EGTA) prior to diphenyl amine analysis.

RESULTS

Examination by TEM revealed that bovine neutrophils exposed to lytic dilutions of LKT had changes consistent with oncosis, whereas neutrophils exposed to sublytic dilutions of LKT and staurosporin, an inducer of apoptosis, had changes consistent with apoptosis. Effects of sublytic dilutions of LKT on apoptosis were confirmed by gel electrophoresis. Replacement of extracellular Ca2+ with EGTA, a Ca2+ chelator, reduced apoptosis attributable to the calcium ionophore A23187, but it did not have significant effects on apoptosis induced by LKT or staurosporin.

CONCLUSIONS AND CLINICAL RELEVANCE

The ability of LKT to cause apoptosis instead of oncosis is concentration-dependent, suggesting that both processes of cell death contribute to an ineffective host-defense response, depending on the LKT concentration in pneumonic lesions. Furthermore, although Ca2+ promotes A23187-induced apoptosis, it is apparently not an essential second messenger for LKT-induced apoptosis.

Preferential externalization of newly synthesized phosphatidylserine in apoptotic U937 cells is dependent on caspase-mediated pathways

Externalization of phosphatidylserine (PtdSer) is a common feature of programmed cell death and plays an important role in the recognition and removal of apoptotic cells. In this study with U937 cells, PtdSer synthesis from [(3)H]serine was stimulated and newly synthesized PtdSer was transferred preferentially to cell-free medium vesicles (CFMV) from cells when apoptosis was induced with a topoisomerase I inhibitor, camptothecin (CAM). When CAM-induced apoptosis was blocked by a caspase inhibitor, z-VAD-fmk, stimulation of PtdSer synthesis and movement to CFMV were abolished. In contrast, changes in synthesis and transport of sphingomyelin (SM) or phosphatidylethanolamine (PtdEtn) were minor; total phosphatidylcholine (PtdCho) synthesis was below control levels. All phospholipids appeared in CFMV but PtdSer displayed a 6-fold increase relative to controls compared to 3-fold for SM, 2-fold for PtdCho and 1.8-fold for PtdEtn. Even greater effects on specificity of PtdSer synthesis, movement to CFMV and inhibition by z-VAD-fmk were observed in apoptotic cells induced by UV irradiation or tumor necrosis factor-alpha/cycloheximide treatment. Thus, PtdSer biosynthesis stimulated during apoptosis in U937 cells was specific for this phospholipid and was correlated with caspase-mediated exposure of PtdSer at the cell surface and preferential movement to vesicles during apoptosis.

Enhanced H(2)O(2)-induced cytotoxicity in "epithelioid" smooth muscle cells: implications for neointimal regression

Vascular smooth muscle cells (SMCs) are phenotypically diverse. Although most medial SMCs can be classified as "fusiform," others are of the "epithelioid" phenotype. Proliferation and apoptosis of epithelioid SMCs may contribute importantly to neointimal formation and regression, respectively. Because reactive oxygen species (ROS) are increased in vascular injury and can induce apoptosis of SMCs, we compared the effects of ROS on epithelioid and fusiform SMCs. Epithelioid and fusiform SMC lines were clonally isolated from rat aortic media and studied under similar conditions and passage numbers. H(2)O(2) produced dose- and time-dependent cytotoxicity that was enhanced in epithelioid compared with fusiform cells. After 24-hour exposure to 50 micromol/L H(2)O(2), epithelioid cell numbers were reduced by 34+/-5% versus a 3+/-5% (P<0.05) reduction in fusiform cell numbers. Similar results were obtained whether H(2)O(2) was administered to growth-arrested or growing cells or when epithelioid and fusiform cells were exposed to extracellular O(2)(.-). To investigate whether apoptosis contributed to enhanced ROS-induced cytotoxicity in epithelioid SMCs, terminal deoxyribonucleotidyl transferase (TDT)-mediated dUTP-digoxigenin nick-end labeling (TUNEL) staining was performed. The incidence of TUNEL positivity was 5-fold increased in epithelioid versus fusiform SMCs after treatment with 50 micromol/L H(2)O(2) (19+/-1% epithelioid versus 5+/-1% fusiform, P<0.05). Enhanced H(2)O(2)-induced apoptosis in epithelioid SMCs was confirmed by DNA laddering. Furthermore, when balloon-injured aortas were exposed to H(2)O(2) ex vivo, enhanced apoptosis was observed in neointimal compared with medial SMCs. These results suggest that epithelioid SMCs exhibit enhanced sensitivity to ROS-induced apoptosis, which may play an important role in neointimal regression.

Apoptosis and the liver

Regulation of the homeostatic balance between cell proliferation and programmed cell death, apoptosis, is essential for development and maintenance of multicellular organisms. Apoptosis is a genetically and evolutionarily highly conserved process. Analysis of the molecular mechanisms of apoptosis has led to a better understanding of many human diseases. Notably in cancer, but also in infectious or autoimmune disease, a deficiency in apoptosis is one of the key events in pathophysiology. On the other hand, overefficient apoptosis, as observed in fulminant liver failure, may be equally harmful for the organism indicating that a tight regulation of the apoptotic machinery is essential for survival. The execution of apoptosis may be initiated by many different signals, either from within or outside the cell involving ligand-receptor interactions, as has been shown for Fas/Fas-ligand, TNF-alpha/TNF-receptor or TGF-beta/TGF-receptor, or potentially by more unspecific signals such as ceramide or DNA damage. During the modulation phase of apoptosis many different genes such as p53, c-myc or Bcl-2/Bax have been shown to able to shift the balance either to cell survival or cell death.

Effects of neoplastic transformation and teniposide (VM26) on protein kinase C isoform expression in rodent fibroblasts

This study examined changes in protein kinase C (PKC) isoforms in rodent fibroblasts (rat F111 and mouse NIH3T3), transformed by the polyoma virus middle T antigen (mT) and undergoing apoptosis in response to teniposide (VM26). The mT-transformed cells up-regulated PKC delta and down-regulated both PKC epsilon and PKC lambda expression, and were more sensitive to the drug than their non-transformed counterparts. The drug treatment further lowered the expression of PKC epsilon, triggered nuclear translocation of PKC delta and its site-specific proteolysis, consistent with the notion that changes in specific PKC isoforms play a role not only in the neoplastic transformation of fibroblasts, but also in their apoptotic response.

The anti-death league: associative control of apoptosis in developing retinal tissue

Apoptosis, the major form of programmed cell death (PCD), is executed through a proteolytic cascade that can be differentially engaged by various extracellular signals. Modulation of both the sensitivity to PCD and of the actual sequence of apoptotic events is, therefore, strongly dependent on cell interactions. This paper reviews the use of a retinal explant preparation as a model of the organized nervous tissue, to study the effects of neural messengers in the control of sensitivity to apoptosis. Studies of retinal explants showed that dopamine, glutamate and nitric oxide may have anti-apoptotic effects upon developing retinal cells. At least the effects of nitric oxide are clearly paracrine. In addition, preliminary evidence has been gathered of a role for gap junctional communication in the control of sensitivity of retinal cells to the induction of apoptosis. These findings underscore the importance of selective cell interactions in the control of PCD in the developing nervous system.

Bisphosphonates induce apoptosis in human breast cancer cell lines

Breast cancer has a prodigious capacity to metastasize to bone. In women with advanced breast cancer and bone metastases, bisphosphonates reduce the incidence of hypercalcaemia and skeletal morbidity. Recent clinical findings suggest that some bisphosphonates reduce the tumour burden in bone with a consequent increase in survival, raising the possibility that bisphosphonates may have a direct effect on breast cancer cells. We have investigated the in vitro effects of bisphosphonates zoledronate, pamidronate, clodronate and EB 1053 on growth, viability and induction of apoptosis in three human breast cancer cell lines (MDA-MB-231, Hs 578T and MCF-7). Cell growth was monitored by crystal violet dye assay, and cell viability was quantitated by MTS dye reduction. Induction of apoptosis was determined by identification of morphological features of apoptosis using time-lapse videomicroscopy, identifying morphological changes in nucleis using Hoechst staining, quantitation of DNA fragmentation, level of expression of bcl-2 and bax proteins and identification of the proteolytic cleavage of Poly (ADP)-ribose polymerase (PARP). All four bisphosphonates significantly reduced cell viability in all three cell lines. Zoledronate was the most potent bisphosphonate with IC50 values of 15, 20 and 3 microM respectively in MDA-MB-231, MCF-7 and Hs 578T cells. Corresponding values for pamidronate were 40, 35 and 25 microM, whereas clodronate and EB 1053 were more than two orders of magnitude less potent. An increase in the proportion of cells having morphological features characteristic of apoptosis, characteristic apoptotic changes in the nucleus, time-dependent increase in the percentage of fragmented chromosomal DNA, down-regulation in bcl-2 protein and proteolytic cleavage of PARP, all indicate that bisphosphonates have direct anti-tumour effects on human breast cancer cells.

Induction of human neutrophil apoptosis by nitric oxide donors: evidence for a caspase-dependent, cyclic-GMP-independent, mechanism

This study investigated the regulatory effects of the major inflammatory mediator, nitric oxide (NO), on human neutrophil apoptosis in vitro. Co-culture of human neutrophils with the NO donors GEA 3162 (1,2,3,4-oxatriazolium,5-amino-3-(3,4-dichlorophenyl)-chloride) (10-100 microM) and 3-morpholino-sydnonimine (SIN-1) (0.3-3 mM) caused a dramatic and concentration-dependent induction of apoptosis. However, N-formyl-methionyl-leucyl-phenylalanine (FMLP)-induced neutrophil activation (actin reorganization and chemotaxis) was inhibited by GEA 3162 treatment. The pro-apoptotic effects of the NO donors were (i) unaffected by the soluble guanylate cyclase inhibitor LY-83583 (6-anilino-5,8-quinolinedione; 100 microM), (ii) antagonized by superoxide dismutase (6 microg/mL), (iii) mimicked by exogenous peroxynitrite (at concentrations >100 microM), and (iv) inhibited by the caspase inhibitor Z-Val-Ala-DL-Asp-fluoromethylketone (100 microM). The pro-apoptotic effect of the NO donors was not mimicked by the cell-permeable cyclic nucleotide analogue, N6,2-O-dibutyrylguanosine-3',5'-cyclic monophosphate (dibutyryl-cGMP) at concentrations < or =0.2 mM. Indeed, at high concentrations (> or =2 mM), dibutyryl-cGMP caused an inhibition of apoptosis. These results suggest that NO-mediated apoptosis, although caspase-dependent, is mediated by a cGMP-independent mechanism and involves the concurrent generation of oxygen free radicals and, potentially, peroxynitrite. Our data reveal a unique role for NO in inflammatory responses with differential effects upon neutrophil activation and survival, with important implications for the successful resolution of inflammation.

The effect of PKC activation on the survival of rat retinal ganglion cells in culture

Natural cell death is a degenerative phenomenon occurring during the development of the nervous system. Approximately half the neurons initially generated during this period die. The role of trophic molecules produced by target and afferent neurons as well as by glial cells controlling this regressive event has been extensively demonstrated. The aim of this work was to study the role of activated protein kinase C (PKC), an enzyme involved in apoptosis regulation, on the survival of retinal ganglion cells kept "in vitro" for 48 h. For this purpose, we used the phorbol 12-myristate 13-acetate (PMA), a tumor promoter agent that activates PKC. Our results showed that PMA increases the survival of ganglion cells. The effect was dose-dependent and PMA concentrations of 10 or 100 ng/ml produced the maximal effect (a two-fold increase on ganglion cells survival compared with 48 h control). This effect was totally abolished by 1.25 microM chelerythrine chloride (an inhibitor of PKC) and 30 microM genistein (an inhibitor of tyrosine kinase enzymes). Otherwise, PMA was effective only when it was chronically present in the cultures. On the other hand, treatment with 20 microM 5-fluoro-2'-deoxyuridine, an inhibitor of cell proliferation, or 25 microM BAPTA-AM, an intracellular calcium chelator, did not block PMA effect. Our results suggest that the survival of retinal ganglion cells "in vitro" may be mediated by a mechanism that involves PKC activation.

Histone H2B phosphorylation in mammalian apoptotic cells. An association with DNA fragmentation

Histone phosphorylation was investigated in several mammalian cells undergoing apoptosis (human HL-60 and HeLa, mouse FM3A and N18 cells, and rat thymocytes). Among the four nucleosomal core histones (H2A, H2B, H3, and H4), H2B, which is not usually phosphorylated in quiescent or growing cells, was found to be phosphorylated after treatment with various apoptotic inducers. The H2B was phosphorylated around the time when nucleosomal DNA fragmentation was initiated and, like this fragmentation, was completely blocked with Z-Asp-CH(2)-DCB, an inhibitor of ICE or ICE-like caspase. The involved single phosphopeptide of H2B proved to be phosphorylatable in vitro with a protein kinase C, and the site Ser-32 was tentatively identified. Despite typical apoptotic chromatin condensation, the H3 phosphorylation was at a low level, and the sites where phosphorylation did occur did not include any mitosis-specific phosphopeptides. Phosphorylation of H4 was increased, but the other two histone proteins (H1 and H2A) were not appreciably changed. These observations imply that 1) H2B phosphorylation occurs universally in apoptotic cells and is associated with apoptosis-specific nucleosomal DNA fragmentation, 2) chromatin condensation in apoptosis occurs by a different biochemical mechanism from those operating during mitosis or premature chromosome condensation, and 3) this unique phosphorylation of H2B is a useful biochemical hallmark of apoptotic cells.