Anticancer drug-induced apoptosis in human monocytic leukemic cell line U937 requires activation of endonuclease(s)

Sensitivity of human prostate cancer cells to chemotherapeutic drugs depends on EndoG expression regulated by promoter methylation

Analysis of promoter sequences of all known human cytotoxic endonucleases showed that endonuclease G (EndoG) is the only endonuclease that contains a CpG island, a segment of DNA with high G+C content and a site for methylation, in the promoter region. A comparison of three human prostate cancer cell lines showed that EndoG is highly expressed in 22Rv1 and LNCaP cells. In PC3 cells, EndoG was not expressed and the EndoG CpG island was hypermethylated. The expression of EndoG correlated positively with sensitivity to cisplatin and etoposide, and the silencing of EndoG by siRNA decreased the sensitivity of the cells to the chemotherapeutic agents in the two EndoG-expressing cell lines. 5-aza-2'-deoxycytidine caused hypomethylation of the EndoG promoter in PC3 cells, induced EndoG mRNA and protein expression, and made the cells sensitive to both cisplatin and etoposide. The acetylation of histones by trichostatin A, the histone deacetylase inhibitor, induced EndoG expression in 22Rv1 cells, while it had no such effect in PC3 cells. These data are the first indication that EndoG may be regulated by methylation of its gene promoter, and partially by histone acetylation, and that EndoG is essential for prostate cancer cell death in the used models.

Kinetics of occurrence of some features of apoptosis during the cryopreservation process of bovine spermatozoa

BACKGROUND

Cryopreservation/thawing of bovine spermatozoa induces a reduction in cell viability and is possibly associated with a form of programmed cell death that we previously named 'apoptosis-like phenomenon'.

METHODS

In this study, we specified, by flow cytometry, the moment of appearance of some characteristics of apoptosis during the cryopreservation process. We also studied the presence and/or activation in bovine sperm cells of specific proteins involved in somatic cell apoptosis by western blot and fluorimetry.

RESULTS

A decrease of the mitochondrial membrane potential (DeltaPsim) was detectable 5 min after sperm dilution in the cryopreservation medium, caspase activation after 3 h of equilibration and an increase in plasma membrane permeability after the complete process of cryopreservation/thawing. The presence of the pro-apoptotic factor Bax, a protein that facilitates the formation of mitochondrial pores, was observed in bovine spermatozoa, but the anti-apoptotic factor Bcl-2 was not detectable. Moreover, it was observed that bovine spermatozoa contain cytochrome c and apoptosis-inducing factor (AIF), two proteins usually released from the mitochondria during the apoptotic process. Activated caspase-9, involved in the mitochondrial pathway, was detected in bovine spermatozoa but not caspase-3 and -8.

CONCLUSIONS

The early features of apoptosis appear as ordered events during the cryopreservation/thawing process of bovine sperm cells. Bovine spermatozoa contain the machinery necessary to proceed to apoptosis involving especially the mitochondrial pathway.

Endonuclease G promotes cell death of non-invasive human breast cancer cells

The invasiveness of breast cancer cells was shown to be associated with the suppressed ability to develop apoptosis. The role of cell death DNases/endonucleases has not been previously examined in relation with the invasiveness of breast cancer cells. We have compared the activity of the endonucleases in seven human breast cancer cell lines different in the level of invasiveness and differentiation. The invasiveness of cell lines was confirmed by an in vitro Matrigel-based assay. The total endonuclease activity in the differentiated non-invasive (WDNI) cell lines was higher than that in the poorly differentiated invasive (PDI) cells. The expression of EndoG strongly correlated with the degree of estrogen receptor expression and showed an inverse correlation with vimentin and matrix metalloproteinase-13. The EndoG-positive WDNI cells were more sensitive to etoposide- or camptothecin-induced cell death than EndoG-negative PDI cells. Silencing of EndoG caused inhibited of SK-BR-3 WDNI cell death induced by etoposide. Human ductal carcinomas in situ expressed high levels of EndoG, while invasive medullar and ductal carcinomas had significantly decreased expression of EndoG. This correlated with decreased apoptosis as measured by TUNEL assay. Our findings suggest that the presence of EndoG in non-invasive breast cancer cells determines their sensitivity to apoptosis, which may be taken into consideration for developing the chemotherapeutic strategy for cancer treatment.

A new role for chondrocytes as non-professional phagocytes. An in vitro study

Chondrocytes are capable of engulfing latex particles, cell detritus, and necrotic and apoptotic remains in vitro. It is conceivable that chondrocytes might be involved in the clearance by phagocytosis of different materials within the cartilage. In fact, so far there is no evidence for the presence of "professional phagocytes" (macrophages and neutrophils) in this tissue. Chondrocyte suspensions obtained from rat knees and hips were cultured to assess phagocytosis of latex particles (1 microm), articular cartilage detritus, and necrotic and apoptotic chondrocyte remains (induced by VP-16 1 mM). We observed that chondrocytes phagocytosed latex particles as evaluated by confocal microscopy and flow cytometry. In addition, we observed that chondrocytes phagocytosed articular cartilage detritus and necrotic and apoptotic VP-16 induced-chondrocytes, as observed by bright field microscopy and transmission electron microscopy.

Cryopreservation Induces an Apoptosis-Like Mechanism in Bull Sperm

Cryopreservation induces many changes in sperm cells, including membrane disorders and cell death. We tested the hypothesis that apoptosis, a form of programmed cell death, can contribute to the fatal effect of cryopreservation on sperm cells. A multiparametric study of apoptosis on bovine sperm is proposed, using flow cytometry, including mitochondrial membrane potential (DeltaPsi(m)), caspase activation, membrane permeability, nucleus condensation, DNA fragmentation, and phosphatidylserine (PS) externalization. The relevance of each test was first validated on a human somatic cell line, U937. Cryopreservation and/or thawing induced significant changes in all apoptotic markers in living bull sperm cells except those concerning the nucleus. After cryopreservation, 44.9% +/- 17% (vs. 11.3% +/- 10.6% before cryopreservation) of sperm cells showed low DeltaPsi(m), 12% +/- 6.3% (vs. 2.2% +/- 1.0% before) contained active caspases, and 10.8% +/- 5.8% (vs. 1.4% +/- 1.1% before) exhibited high membrane permeability. However, cryopreservation had no effect on DNA fragmentation (9.1% +/- 7.7% before vs. 11.1% +/- 5.7% after cryopreservation) or on nucleus condensation (46% +/- 12.7% before vs. 43.8% +/- 13.1% after). Cryopreservation acts as an apoptotic mechanism inducer in bovine sperm cells, where the earliest but not the latest features of cells undergoing apoptosis occur. We have named this abortive process an apoptosis-like phenomenon.

IC101 induces apoptosis by Akt dephosphorylation via an inhibition of heat shock protein 90-ATP binding activity accompanied by preventing the interaction with Akt in L1210 cells

To find novel pharmacological tools useful for analyzing the molecular mechanism of apoptosis from natural resources, in the present study, we examined the activity of IC101, a cyclic depsipeptide isolated from Streptomyces sp. MJ202-72F3, to induce apoptosis in the L1210 cell line. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed that IC101 caused a concentration-dependent cell death with a 50% effective concentration value of 20 nM. Cell shrinkage, chromatin condensation, a typical DNA ladder pattern, and up-regulation of cleaved caspase-3 expression, which were biochemical characteristics of apoptosis, were induced by IC101. It also was observed that IC101 caused a concentration-dependent dephosphorylation of Akt and Bad without affecting phosphatidylinositol-3 kinase, an upstream molecule of Akt. IC101 dephosphorylated the 90-kDa protein, as assayed by immunblotting of the cell extract by using anti-phosphotyrosine antibody. To identify the 90-kDa protein, immunoprecipitation and direct nano-flow liquid chromatography-tandem mass spectrometry (LC-MS) were performed to demonstrate that this protein was heat shock protein 90 (HSP90). Consistently, it was observed that IC101 induced the HSP90 tyrosine dephosphorylation by immunoblot analysis of immunoprecipitates with anti-HSP90 antibody using anti-phosphotyrosine antibody. IC101 caused the degradation of Raf-1, which formed a complex with HSP90. The HSP90-ATP binding also was inhibited by IC101 in a noncompetitive manner. An interaction of HSP90 with Akt was shown to be inhibited by IC101 in a concentration-dependent manner. These results suggest that IC101 dephosphorylates Akt through an inhibition of HSP90 functions, resulting in the interaction with Akt to induce apoptotic cell death of L1210 cells.

The combination of the antitumoural pyridyl cyanoguanidine CHS 828 and etoposide in vitro--from cytotoxic synergy to complete inhibition of apoptosis

1. The present study was aimed at elucidating the apoptosis inhibitory properties of the cyanoguanidine CHS 828. CHS 828 exhibits impressive cytotoxic activity in vitro and in vivo. Apoptosis is not its main mode of cytotoxic effect, and we have previously proposed a dual mechanism, where CHS 828 inhibits its own cell death pathways. 2. Etoposide on the other hand, is a well-established anticancer agent with documented effect in a number of malignancies, induces apoptosis through extensively studied caspase dependent pathways. 3. Here we studied the combined effect of the two drugs in the human lymphoma cell line U-937 GTB. Cytotoxicity was evaluated as total viability measured by the fluorometric microculture cytotoxicity assay (FMCA). Caspase activity was assessed by colorimetric detection of specific cleavage products for caspases 3, 8 and 9, respectively. Morphology was evaluated in May-Grünwald/Giemsa stained preparations. Interaction analysis based on FMCA results of simple combination exposure revealed impressive synergistic effect on cell kill. 4. Detailed investigations of the kinetics involved showed that short pre-exposure (0-12 h) to CHS 828 enhanced caspase activation by etoposide, while longer pre-exposure (18-48 h) inhibited both caspase activation and apoptotic morphology otherwise induced by etoposide. The present results support the theory that CHS 828 block specific cell death pathways. 5. The synergistic results are promising for future combination trials in animals, however, different dosing schedules should be considered, in order to investigate whether the above findings translate into the in vivo setting.

Aurintricarboxylic acid protects against cell death caused by lipopolysaccharide in macrophages by decreasing inducible nitric-oxide synthase induction via IkappaB kinase, extracellular signal-regulated kinase, and p38 mitogen-activated protein kinase inhibition

To elucidate the mechanisms involved in cell protection by aurintricarboxylic acid (ATA), an endonuclease inhibitor, high nitric oxide (NO)-induced macrophage apoptosis was studied. In RAW 264.7 macrophages, a high level of NO production accompanied by cell apoptosis was apparent with lipopolysaccharide (LPS) treatment. Direct NO donor sodium nitroprusside (SNP) also dramatically induced cell death, with an EC(50) of 1 mM. Coincubation of ATA (1-500 microM) in LPS-stimulated RAW 264.7 cells resulted in a striking reduction of NO production and cell apoptosis, whereas only a partial cell protection was achieved in response to SNP. This suggests that abrogation of inducible nitric-oxide synthase (iNOS)-dependent NO production might contribute to ATA protection of LPS-treated cells. Immunoblotting and reverse transcription-polymerase chain reaction analysis revealed that ATA down-regulated iNOS protein through transcriptional inhibition of iNOS gene expression but was unrelated to iNOS protein stability. ATA not only inhibited nuclear factor-kappaB (NF-kappaB) activation through impairment of the targeting and degradation of IkappaBs but also reduced LPS-induced activator protein-1 (AP-1) activation. These actions of ATA were not caused by the influence on LPS binding to macrophage membrane. Kinase assays indicated that ATA inhibited IkappaB kinase (IKK), extracellular signal-regulated kinase (ERK), and p38 mitogen-activated protein kinase (MAPK) activity both in vivo and in vitro, suggesting a direct interaction between ATA and these signaling molecules. Taken together, these results provide novel action targets of ATA and indicate that ATA protection of macrophages from LPS-mediated cell death is primarily the result of its inhibition of NO production, which closely relates to the inactivation of NF-kappaB and AP-1 and inhibition of IKK, ERK and p38 MAPK.

Characteristics of etoposide-induced apoptotic cell death in the U-937 human lymphoma cell line

Cell death induced by etoposide in the human lymphoma cell line U-937 GTB was characterized. Activity of caspases -3, -8 and -9 was measured by spectrophotometric detection of specific cleavage products, DNA fragmentation by TdT-mediated dUTP nick end-labelling (TUNEL), and apoptotic morphology by conventional staining and microscopy, as well as by a novel method-the microculture kinetics (MiCK) assay. Synthesis of protein and DNA during exposure was monitored by incorporation of radioactive leucine and thymidine, respectively. The effects of caspase inhibitors on total viability, as well as early and late morphological changes were studied. Etoposide rapidly induced apoptosis, dependent on caspase-3 and -8, but inhibition of these caspases did not prevent major cell death, but promoted a switch in late morphology. The novel MiCK assay added valuable information on early morphological events during cell death. Hence, this study provides support for caspase-8-mediated apoptosis in U-937 GTB when exposed to etoposide. General caspase inhibition switches cell death to one with a different morphology.

Cell death with atypical features induced by the novel antitumoral drug CHS 828, in human U-937 GTB cells

N-(6-(4-chlorophenoxy)hexyl)-N'-cyano-N"-4-pyridylguanidine (CHS 828), with promising antitumoral effects in vitro and in vivo, is currently in clinical Phase I and II studies. Its exact mechanism of action is unclear, but previous studies indicate that CHS 828 induces a controlled, delayed mode of cell death. The characteristics of the cell death process were investigated in vitro in the apoptosis-prone cell line U-937 GTB. Mitochondria showed hyperpolarization at 24 to 32 h and a subsequent late disruption of mitochondria membrane potential (Deltapsi(m)). Between 44 and 72 h of CHS 828 exposure, there was an increasing frequency of terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick end labeling (TUNEL) positive cells indicative of apoptosis, but caspase-3 was only modestly increased and caspases-8 and -9 showed no activation upon CHS 828 exposure. Furthermore, the morphology of exposed cells did not conform to classical apoptosis, and viability and morphology were unaffected by inhibition of caspases. Thus, CHS 828 induces several unexpected features in this system, suggesting a potentially novel mechanism of action.

Temporal effects of the novel antitumour pyridyl cyanoguanidine (CHS 828) on human lymphoma cells

CHS 828, a novel pyridyl cyanoguanidine, has shown potent antitumour activity both in vitro and in vivo and is currently undergoing phase I evaluation in humans in collaboration with the European Organization for Research and Treatment of Cancer (EORTC). Here we study the temporal effects of CHS 828 on cytotoxicity, protein and DNA synthesis, cellular morphology and ultra structure using the lymphoma cell line U-937 GTB as the primary tumour model. In vitro analysis of tumour cell survival in response to CHS 828 revealed a cytotoxic effect progressively increased as a function of exposure time with maximum efficacy observed after 72 h. Activity of CHS 828 on U-937 GTB cells grown in vivo was also found. CHS 828 induced-cell death was dependent on intact protein synthesis and most cells appeared to lose their membrane integrity in the presence of a relatively well preserved nuclear structure. The results indicate that CHS 828 induced active and delayed cell death with a non-apoptotic morphology.