Disruption of mitochondria is an early event during dolichyl monophosphate-induced apoptosis in U937 cells

The role of cholesterol metabolism in leukemia

Leukemia is a common hematological malignancy with overall poor prognosis. Novel therapies are needed to improve the outcome of leukemia patients. Cholesterol metabolism reprogramming is a featured alteration in leukemia. Many metabolic-related genes and metabolites are essential to the progress and drug resistance of leukemia. Exploring potential therapeutical targets related to cholesterol homeostasis is a promising area. This review summarized the functions of cholesterol and its derived intermediate metabolites, and also discussed potential agents targeting this metabolic vulnerability in leukemia.

Involvement of the mitogen-activated protein kinase pathway in soft-shelled turtle iridovirus-induced apoptosis

Iridoviruses are large DNA viruses that infect invertebrates and poikilothermic vertebrates, and result in significant economic losses in aquaculture production, and drastic declines in amphibian populations. Soft-shelled turtle iridovirus (STIV) is the causative agent of severe systemic diseases in farm-raised soft-shelled turtles (Trionyx sinensis). In the present study, the mechanisms of STIV-induced cell death and the roles of the mitogen-activated protein kinase (MAPK) signaling pathway were investigated. STIV infection evoked typical apoptosis in fish cells, as demonstrated by the formation of apoptotic bodies, positive terminal deoxynucleotidyl transferase-mediated nicked-end labeling, and caspase-3 activation. The translocation of cytochrome c from mitochondria to cytoplasm, and caspase-9 activation suggested that a mitochondria-mediated pathway was involved in STIV-induced apoptosis. Moreover, MAPK pathways, including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK) and p38 MAPK signaling were activated during STIV infection. Using specific inhibitors, we found that MAPK signaling molecules, including ERK, JNK and p38 MAPK, were important for virus release, whereas, only ERK and p38 MAPK were involved in STIV-induced apoptosis by modulating caspase-3 activity. Taken together, our findings shed light on the roles of the MAPK signaling pathway in iridovirus-induced apoptosis and virus replication, which provides new insights into understanding iridovirus-host interaction.

Cytotoxicity, hydrophobicity, uptake, and distribution of osmium(II) anticancer complexes in ovarian cancer cells

The cytotoxicity, hydrophobicity (log P), cellular uptake, aqueous reactivity, and extent of DNA adduct formation in the A2780 ovarian carcinoma cells for four osmium(II) arene complexes [(eta(6)-arene)Os(4-methyl-picolinate)Cl] that differ only in their arene ligands as benzene (1), p-cymene (2), biphenyl (3), or tetrahydroanthracene (4) are reported. There is a correlation between hydrophobicity (log P), cellular uptake, nucleus uptake, and cytotoxicity of the complexes, following the order 3 approximately 4 > 2 > 1, suggesting that the arene plays an important role in the biological activity of these types of compounds. Cell distribution studies using fractionation showed that all four compounds distribute similarly within cells. DNA binding of osmium did not correlate with cytotoxicity, indicating that the nature of the DNA lesion may also be crucial to activity. TEM images of ovarian cells treated with 3 revealed morphological changes associated with apoptosis with possible involvement of mitochondria.

Peroxisome proliferator-activated receptor gamma ligands stimulate myeloid differentiation and lipogenensis in human leukemia NB4 cells

Peroxisome proliferator-activated receptor gamma (PPARgamma) plays a central role in adipocyte and macrophage differentiation. Pioglitazone (Actos, AD4833), an antidiabetic drug, and 15-deoxy-Delta(12,14)-prostaglandin J2 (PGJ2) have recently been identified as synthetic and natural ligands for PPARgamma, respectively. In this study, we examined the effects of PPARgamma ligands on differentiation and lipogenesis in promyelocytic leukemia NB4 cells, in which PPARgamma protein was expressed and ligand-stimulated PPARgamma-specific transcription of adipocyte fatty-acid binding protein was confirmed. Treatment with PPARgamma ligand (AD4833 or PGJ2) alone markedly suppressed proliferation but did not induce differentiation. The combined treatment of the cells with PPARgamma ligand and all-trans retinoic acid (ATRA) synergistically induced myelocytic differentiation, as determined by nitroblue tetrazolium reducing ability and cell morphology. During these processes of differentiation, we observed marked accumulation of lipid droplets in the cytoplasm. The cellular triacylglycerol levels increased 2.7-fold after treatment with the inducers. Simultaneously, BODIPY-fatty acid was incorporated into the cytosol and concentrated in lipid droplets. The biosynthesis of triacylglycerol-containing BODIPY-fatty acids was increased twofold in differentiated cells. These findings clearly demonstrate that treatment with PPARgamma ligands not only induced differentiation but also stimulated lipogenesis in NB4 cells, indicating a close association between differentiation and lipogenesis in PPARgamma-stimulated human myeloid cells.

Changes in intracellular electrolyte concentrations during apoptosis induced by UV irradiation of human myeloblastic cells

Decreases in the intracellular concentrations of both K+and Cl−have been implicated in playing a major role in the progression of apoptosis, but little is known about the temporal relationship between decreases in electrolyte concentration and the key events in apoptosis, and there is no information about how such decreases affect different intracellular compartments. Electron probe X-ray microanalysis was used to determine changes in element concentrations (Na, P, Cl, and K) in nucleus, cytoplasm, and mitochondria in U937 cells undergoing UV-induced apoptosis. In all compartments, the initial stages of apoptosis were characterized by decreases in [K] and [Cl]. The largest decreases in these elements were in the mitochondria and occurred before the release of cytochrome c. Initial decreases in [K] and [Cl] also preceded apoptotic changes in the nucleus. In the later stages of apoptosis, the [K] continued to decrease, whereas that of Cl began to increase toward control levels and was accompanied by an increase in [Na]. In the nucleus, these increases coincided with poly(ADP-ribose) polymerase cleavage, chromatin condensation, and DNA laddering. The cytoplasm was the compartment least affected and the pattern of change of Cl was similar to those in other compartments, but the decrease in [K] was not significant until after active caspase-3 was detected. Our results support the concept that normotonic cell shrinkage occurs early in apoptosis, and demonstrate that changes in the intracellular concentrations of K and Cl precede apoptotic changes in the cell compartments studied.

Alterations in mitochondrial morphology are associated with hyperthermia-induced apoptosis in early postimplantation mouse embryos

BACKGROUND

Previously, we showed that teratogens such as hyperthermia activate the mitochondrial apoptotic pathway in day nine mouse embryos. Activation of this pathway involves an initial release of cytochrome c from intermembranous spaces of the mitochondria into the cytoplasm. Cytoplasmic cytochrome c then activates a caspase cascade resulting in the orderly demise of the cell. In addition, we showed that teratogens activate the mitochondrial pathway in cells of the neuroepithelium, but not the heart.

METHODS

To further investigate the role of the mitochondrion in teratogen-induced apoptosis, we used transmission electron microscopy (TEM) to compare mitochondrial morphology in cells of the neuroepithelium and heart of control and hyperthermia-treated embryos. Because we know that the apoptotic pathway is activated some time during the first 5 hr after teratogen exposure is initiated, we assessed mitochondrial morphology at 1, 2.5, and 5 hr after day nine mouse embryos were exposed to hyperthermia (43 degrees C, 15 min).

RESULTS

In neuroepithelial cells of the prosencephalon, abnormally-shaped mitochondria were observed at the 1 hr time point and thereafter, whereas loss of cristae and shrunken mitochondria were noted at the 5 hr time point. In contrast, no obvious changes in mitochondria of heart cells were observed at any of the time points monitored.

CONCLUSIONS

These results indicate that teratogen-induced cell death in neuroepithelial cells is temporally correlated with alterations in mitochondrial morphology, whereas the absence of cell death in the heart is correlated with a corresponding lack of change in mitochondrial morphology. Birth Defects Research (Part A), 2003.

Biological effects of epicuticular flavonoids from Primula denticulata on human leukemia cells

The biological effects of epicuticular substances in farinose exudates accumulated on inflorescence shafts and calyces of Primula denticulata on human acute myeloid leukemia cells (HL-60) were analyzed. The crude material possessed little antioxidative capacity but strong cytostatic properties. Some of its known components (5-hydroxyflavone, 2'-hydroxyflavone, 5,2'-dihydroxyflavone, and 5,8-dihydroxyflavone) were further tested to identify the biologically active compounds. The effects of these flavones on cell cycle progression, mitochondrial membrane potential, and reactive oxygen species have been investigated by flow cytometry. The flavonol quercetin was included in the study as reference compound because of its known cytostatic properties and its activity as radical scavenger. Compared to quercetin the flavones induced little apoptosis (up to 40 microM), but despite their low toxicity, the Primula flavonoids possessed strong cytostatic properties even at low concentrations. The cell cycle distribution showed a characteristic time-dependent shift, giving evidence of a generally short-lived effect of the test compounds in the exposed cells. The antioxidative properties quantified according to two different methods correlated with the number of hydroxyl groups. Whereas quercetin strongly affected the mitochondrial membrane potential, none of the Primula flavones showed a comparable effect.

Ham-Wasserman Lecture

Conventional treatment of acute leukemia involves the use of cytotoxic agents (chemotherapy), but other strategies have been explored. All-trans retinoic acid (ATRA) and arsenic have clearly been effective in the treatment of acute promyelocytic leukemia (APL), which creates the possibility that other types of acute leukemia can be conquered by selectively inducing differentiation and/or apoptosis. A great number of investigations have been performed to elucidate the mechanisms and search for effective agents in the treatment of other types of acute leukemia by these new strategies. Progress at the molecular level has been achieved in explaining the mechanisms of action of ATRA and arsenic compounds, and several new agents have emerged, although their clinical effectiveness remains to be confirmed. Mechanism-/gene-based targeted therapy and a combination of different strategies will improve the treatment of acute leukemia.

Ham-Wasserman Lecture

Conventional treatment of acute leukemia involves the use of cytotoxic agents (chemotherapy), but other strategies have been explored. All-trans retinoic acid (ATRA) and arsenic have clearly been effective in the treatment of acute promyelocytic leukemia (APL), which creates the possibility that other types of acute leukemia can be conquered by selectively inducing differentiation and/or apoptosis. A great number of investigations have been performed to elucidate the mechanisms and search for effective agents in the treatment of other types of acute leukemia by these new strategies. Progress at the molecular level has been achieved in explaining the mechanisms of action of ATRA and arsenic compounds, and several new agents have emerged, although their clinical effectiveness remains to be confirmed. Mechanism-/gene-based targeted therapy and a combination of different strategies will improve the treatment of acute leukemia.