Caspase-3-dependent and caspase-3-independent pathways leading to chromatin DNA fragmentation in HL-60 cells

Apoptosis induced by etoposide (VP-16) in HL-60 cells was confirmed to be caspase-dependent. It was fully inhibited by the broad-spectrum caspase inhibitor Z-VAD-fmk. However, the caspase-3-specific inhibitor Z-DEVD-fmk only partially inhibited apoptosis. This indicated that a second caspase is required in vivo for full activation of the apoptotic nucease CAD. Aurin tricarboxylic acid (ATA) did not inhibit VP-16-induced apoptosis. In contrast, apoptosis induced by hydroxychloroquine (HCQ) in HL-60 cells was caspase-3 independent and was fully inhibited by ATA. Thus, CAD does not appear to be involved in chromatin DNA degradation in this case. A second apoptotic nuclease is postulated to degrade the DNA, likely endo-exonuclease, an abundant nuclear enzyme that acts on both DNA and RNA and is present in latent form. HCQ, but not VP-16, stimulated DNA degradation (laddering) in isolated nuclei. This indicates that the drug can act directly in the nuclei to trigger activation of the second latent apoptotic nuclease.     

Caspase-3 activates endo-exonuclease: Further evidence for a role of the nuclease in apoptosis

Single-strand DNase and poly rAase, activities characteristic of endo-exonuclease, were co-activated in nuclear fractions of HL-60 cells by caspase-3. Activation was accompanied by cleavages of large soluble polypeptides (130–185 kDa) and a 65 kDa inactive chromatin-associated polypeptide related to the endo-exonuclease of Neurospora crassa as detected on immunoblots. The major products seen in vitro were a 77 kDa soluble polypeptide and an active chromatin-associated 34 kDa polypeptide. When HL-60 cells were induced to undergo apoptosis by treating with 50 M etoposide (VP-16) for 4 hours, 77 kDa and 40 kDa polypeptides accumulated in nuclear fractions. Chromatin DNA fragmentation activity was also activated in cytosol and nuclear extract either by pre-treating the cells in vivo with VP-16 or by treating the cytosol in vitro with caspase-3 or dATP and cytochrome c. Endo-exonuclease activated by caspase-3 in cytosol-derived fractions augmented chromatin DNA fragmentation activity in vitro. Endo-exonuclease is proposed to act in vivo in conjunction with the caspase-activated DNase (CAD) to degrade chromatin DNA during apoptosis of HL-60 cells.     

Characterization of apoptosis-like endonuclease activity in avian thymocytes.

In the current study the internucleosomal DNA cleavage activity associated with apoptosis was investigated in avian thymocytes. Thymocyte nuclear proteins from glucocorticoid-treated chickens were incubated with chicken red blood cell (cRBC) nuclei, and DNA degradation was analyzed by agarose gel electrophoresis and fluorescence-activated flow cytometry. The thymocyte nuclear extract contained an endonuclease activity that degraded cRBC chromatin at internucleosomal sites as detected by agarose gel electrophoresis. Flow cytometry analysis of cRBC nuclei that were treated with thymocyte nuclear proteins demonstrated a loss of cellular DNA as a function of the amount of added nuclease activity. Furthermore, it was demonstrated that the thymocyte nuclear extract contained a nuclease activity that was capable of degrading radiolabelled naked 32P-DNA into acid soluble DNA fragments. All three assay methods demonstrate that the thymocyte nuclease activity can be inhibited by EDTA, zinc ions and the nuclease inhibitor aurintricarboxylic acid. Based on the analysis of cofactor requirement of this nuclease activity and its susceptibility to inhibitors, the endonuclease activity present in avian apoptotic thymocytes appears to be identical to the mammalian counterpart.     

苏云金芽孢杆菌Bt9875晶体蛋白诱导HL-60细胞凋亡

[目的]研究苏云金芽孢杆菌(Bacillus thuringiensis,Bt)Bt9875菌株晶体蛋白对人急性髓细胞性白血病细胞HL-60的影响.[方法]采用MTT比色、荧光显微观察、DNA凝胶电泳、流式细胞术等方法来检测不同浓度的Bt9875晶体蛋白处理后HL-60细胞的凋亡特征.[结果]Bt9875晶体蛋白对HL-60细胞的生长具有明显的抑制作用,且随着蛋白质浓度的增加对HL-60细胞生长抑制愈加明显,而对正常人外周血单个核细胞(PBMC)无作用;荧光显微镜下观察发现经该蛋白作用后HL-60细胞核的形态呈现凋亡特征;流式细胞术分析表明,HL-60细胞经100 μg/mL晶体蛋白作用后,凋亡率达到52%;琼脂糖凝胶电泳显示细胞DNA呈梯状降解.[结论]初步证明了Bt9875晶体蛋白在体外能够明显抑制HL-60细胞的增长,并诱导其凋亡,这为苏云金芽抱杆菌晶体蛋白的应用开创了新的思路.     

Properties of condensed chromatin in barley nuclei

A method for isolation and purification of intact nuclei from barley leaves was developed and several properties of the chromatin were studied. The dense structure of the main part of the chromatin does not alter the accessibility of the DNA to nucleases. 60% of the nuclear DNA can be degraded by micrococcal endonuclease. Nevertheless the solubility of the chromatin fragments depends on the extent of nuclease digestion; solubilisation occurring only when the major part of the internucleosomal DNA was degraded (30% of digestion). Electron microscopic observations suggest that this was due to particularly dense organization of the chromatin in situ. The possible physiological meaning of some of these properties are discussed.     

Quantitative determination of apoptosis on leukemia cells by infrared spectroscopy

Quantitation of apoptotic cell death in vivo has become an important issue for patients with acute leukemia. We describe herein a new analytical method, based on infrared (IR) spectroscopy, to estimate the percentage of apoptotic leukemic cells in two different cell lines (CEM and K562), induced with etoposide (VP-16). As the percentage of apoptosis increases, the protein structure shifts from dominantly -sheet to unordered (random coil), the overall lipid content increases and the amount of detectable DNA decreases. These changes can be directly related to the percentage of apoptosis as determined by two standard reference methods: flow cytometry and DNA ladder formation. The correlation between the significant IR spectral changes and the percentage of apoptotic leukemia cells in the two cell lines was optimal up to 24 h following etoposide treatment (r = 0.99 for CEM cells and r = 0.96 for K562 cells). Furthermore, IR spectroscopy is able to detect apoptotic changes in these cells already after 4 h treatment with VP-16, compared to flow cytometry which needs 6 h to observe significant changes. Our study suggests that IR spectroscopy may have potential clinical utility for the early, fast and reagent free assessment of chemotherapeutic efficacy in patients with leukemia.     

NK4拮抗HGF促进肿瘤细胞凋亡的生物学效应

观察NK4通过拮抗肝细胞生长因子（HGF）诱导不同肿瘤细胞凋亡,研究其生物学作用及分子机制.以足叶乙甙（VP-16）诱导凋亡,分别或经HGF蛋白、NK4蛋白处理5种肿瘤细胞（B细胞淋巴瘤细胞系Raji、人急性粒细胞白血病细胞系HL-60、宫颈癌细胞系HeLa、前列腺癌细胞系PC-3、非小细胞肺癌细胞系A549）,采用流式细胞术（FCM）、吖啶橙 (AO) 染色法、苏木素 伊红（HE）染色法定量观察5种肿瘤细胞的凋亡情况,并进行相关分析. FCM发现,经VP-16处理5种肿瘤细胞凋亡率均显著高于对照组(P<0.001),而HGF+VP-16组凋亡率明显下降(P<0.01),HGF+NK4+VP-16组细胞凋亡率均明显高于HGF+VP-16组(P<0.05). AO染色和HE染色结果也证实,5种肿瘤细胞经VP-16处理后凋亡率均显著增高 (P<0.001,P<0.001),而HGF+VP-16组细胞凋亡率均明显低于VP-16组(P<0.001,P<0.01), HGF+NK4+VP-16组细胞凋亡率均明显高于HGF+VP-16组(P<0.001,P<0.05).此外,发现NK4+VP-16组、HGF+ NK4+VP-16组、VP-16组等3组间凋亡率无统计学差异(P>0.05). 以上结果提示,HGF蛋白可抵抗凋亡诱导剂VP-16的作用, 明显降低细胞凋亡;NK4通过竞争性抑制HGF从而促进肿瘤细胞的凋亡,具有潜在的肿瘤治疗价值.     

Nelfinavir,an HIV-1 Protease Inhibitor,Induces Oxidative Stress–Mediated,Caspase-Independent Apoptosis in Leishmania Amastigotes

Background

Visceral leishmaniasis has now emerged as an important opportunistic disease in patients coinfected with human immunodeficiency virus type-1 (HIV-1). Although the effectiveness of HIV-1 protease inhibitors, such as nelfinavir, in antiretroviral therapies is well documented, little is known of the impact of these drugs on Leishmania in coinfected individuals.

Methodology and Principal Findings

Here, we show that nelfinavir generates oxidative stress in the parasite, leading to altered physiological parameters such as an increase in the sub-G1 DNA content, nuclear DNA fragmentation and loss of mitochondrial potential, which are all characteristics of apoptosis. Pretreatment of axenic amastigotes with the caspase inhibitor z-VAD-fmk did not inhibit the increase in sub-G1 DNA content in nelfinavir-treated parasites, suggesting therefore that this antiviral agent does not kill Leishmania amastigotes in a caspase-dependent manner. Furthermore, we observed that the mitochondrial resident protein endonuclease G is involved. We also demonstrate that parasites overexpressing GSH1 (the rate limiting enzyme of glutathione biosynthesis) were more resistant to nelfinavir when compared to untransfected controls.

Conclusions and Significance

These data suggest that nelfinavir induces oxidative stress in Leishmania amastigotes, culminating in caspase-independent apoptosis, in which DNA is degraded by endonuclease G. This study provides a rationale for future, long-term design of new therapeutic strategies to test nelfinavir as a potential antileishmanial agent as well as for possible future use in Leishmania/HIV-1 coinfections.     

The sorcin-annexin VII calcium-dependent interaction requires the sorcin N-terminal domain

Dolichyl monophosphate (Dol-P) has been found to induce apoptosis in human leukemia U937 cells. During this apoptotic execution, the increase of plasma membrane fluidity (5–20 min), caspase-3-like protease activation (2–4 h), chromatin condensation and DNA ladder formation (3–4 h) were observed successively. Here, we report that reduction in mitochondrial transmembrane potential and translocation of apoptosis-inducing factor (AIF) are early events (1–3 h) in the apoptotic process induced by Dol-P in U937 cells. The AIF was concentrated around nuclei and partly translocated to the nuclei, which was confirmed by immunocytochemistry using specific anti-AIF antibody. Both caspase-8 and caspase-3 inhibitors blocked only DNA fragmentation but not mitochondrial processes, AIF migration and chromatin condensation. These results indicate that mitochondrial changes are an early step in the apoptosis induced by Dol-P and AIF is one of the important factors which induce chromatin condensation in nuclei.     

Dihydroartemisinin (DHA) induces caspase-3-dependent apoptosis in human lung adenocarcinoma ASTC-a-1 cells

Background

Dihydroartemisinin (DHA), a semi-synthetic derivative of artemisinin, isolated from the traditional Chinese herb Artemisia annua, is recommended as the first-line anti-malarial drug with low toxicity. DHA has been shown to possess promising anticancer activities and induce cancer cell death through apoptotic pathways, although the molecular mechanisms are not well understood.

Methods

In this study, cell counting kit (CCK-8) assay was employed to evaluate the survival of DHA-treated ASTC-a-1 cells. The induction of apoptosis was detected by Hoechst 33258 and PI staining as well as flow cytometry analysis. Collapse of mitochondrial transmembrane potential (ΔΨ_m) was measured by dynamic detection under a laser scanning confocal microscope and flow cytometry analysis using Rhodamine123. Caspase-3 activities measured with or without Z-VAD-fmk (a broad spectrum caspase inhibitor) pretreatment by FRET techniques, caspase-3 activity measurement, and western blotting analysis.

Results

Our results indicated that DHA induced apoptotic cell death in a dose- and time-dependent manner, which was accompanied by mitochondrial morphology changes, the loss of ΔΨ_m and the activation of caspase-3.

Conclusion

These results show for the first time that DHA can inhibit proliferation and induce apoptosis via caspase-3-dependent mitochondrial death pathway in ASTC-a-1 cells. Our work may provide evidence for further studies of DHA as a possible anticancer drug in the clinical treatment of lung adenocarcinoma.     

Behavior of organelle nuclei (nucleoids) in generative and vegetative cells during maturation of pollen inLilium longiflorum andPelargonium zonale

Summary The behavior of organelle nuclei during maturation of the male gametes ofLilium longiflorum andPelargonium zonale was examined by fluorescence microscopy after staining with 4,6-diamidino-2-phenylindole (DAPI) and Southern hybridization. The organelle nuclei in both generative and vegetative cells inL. longiflorum were preferentially degraded during the maturation of the male gametes. In the mature pollen grains ofL. longiflorum, there were absolutely no organelle nuclei visible in the cytoplasm of the generative cells. In the vegetative cells, almost all the organelle nuclei were degraded. However, in contrast to the situation in generative cells, the last vestiges of organelle nuclei in vegetative cells did not disappear completely. They remained in evidence in the vegetative cells during germination of the pollen tubes. InP. zonale, however, no evidence of degradation of organelle nuclei was ever observed. As a result, a very large number of organelle nuclei remained in the sperm cells during maturation of the pollen grains. When the total DNA isolated from the pollen or pollen tubes was analyzed by Southern hybridization with a probe that contained therbc L gene, for detection of the plastid DNA and a probe that contained thecox I gene, for detection of the mitochondrial DNA, the same results were obtained. Therefore, the maternal inheritance of the organelle genes inL. longiflorum is caused by the degradation of the organelle DNA in the generative cells while the biparental inheritance of the organelle genes inP. zonale is the result of the preservation of the organelle DNA in the generative and sperm cells. To characterize the degradation of the organelle nuclei, nucleolytic activities in mature pollen were analyzed by an in situ assay on an SDS-DNA-gel after electrophoresis. The results revealed that a 40kDa Ca²⁺-dependent nuclease and a 23 kDa Zn²⁺ -dependent nuclease were present specifically among the pollen proteins ofL. longiflorum. By contrast, no nucleolytic activity was detected in a similar analysis of pollen proteins ofP. zonale.     

Kinetics of nuclease digestion of Physarum polycephalum nuclei at different stages of the cell cycle

The kinetics of nuclease digestion of Physarum polycephalum nuclei by staphylococcal nuclease and DNase I has been studied at different stages of the cell cycle. Significant differences in the digestion behaviour of nuclei from metaphase and interphase have been detected with DNase I but not with staphylococcal nuclease. Furthermore the structure of newly replicated DNA in S phase differs from the bulk in that it is more easily degraded to acid-soluble products by either staphylococcal nuclease or by DNAase I. At least four types of chromatin structure can be distinguished by our digestion kinetics experiments.     

Mechanism for generation of hydrogen peroxide and change of mitochondrial membrane potential during rotenone-induced apoptosis

Rotenone, an inhibitor of NADH dehydrogenase complex, is a naturally occurring insecticide, which is capable of inducing apoptosis. Rotenone-induced apoptosis is considered to contribute to its anticancer effect and the etiology of Parkinson's disease (PD). We demonstrated that rotenone induced internucleosomal DNA fragmentation, DNA ladder formation, in human cultured cells, HL-60 (promyelocytic leukemia) and BJAB cells (B-cell lymphoma). Flow cytometry showed that rotenone induced H2O2 generation, followed by significant changes in the mitochondrial membrane potential (DeltaPsim). Caspase-3 activity increased in HL-60 cells in a time-dependent manner. These apoptotic events were delayed in HP100 cells, an H2O2-resistant clone of HL-60, confirming the involvement of H2O2 in apoptosis. Expression of anti-apoptotic protein, Bcl-2, in BJAB cells drastically inhibited DeltaPsim change and DNA ladder formation but not H2O2 generation, confirming the participation of mitochondrial dysfunction in apoptosis. NAD(P)H oxidase inhibitors prevented H2O2 generation and DNA ladder formation. These results suggest that rotenone induces O2(-)-derived H2O2 generation through inhibition of NADH dehydrogenase complex and/or activation of NAD(P)H oxidase, and H2O2 generation causes the disruption of mitochondrial membrane in rotenone-induced apoptosis.     

Apoptosis of unstimulated human lymphocytes and DNA strand breaks induced by the topoisomerase II inhibitor etoposide (VP-16)

Etoposide (VP-16)-induced DNA strand breaks and repair and apoptosis of unstimulated human lymphocytes have been studied using DNA comet assay, electrophoresis of low-molecular-weight DNA extracts, and fluorescence microscopy. Incubation of unstimulated human lymphocytes with VP-16 (50-200 microg/ml) for 3 or 24 h induced apoptosis. This conclusion is supported by results of morphological studies, evaluation of the proportion of hypodiploidy and internucleosomal degradation of DNA in lymphocytes. Etoposide-induced formation of DNA strand breaks preceded the appearance of these conventional apoptotic manifestations. The number of single-strand breaks depended on VP-16 concentration, and 2-3 h after its removal from the incubation medium they were repaired. The hydroxyl group at the C-4; position of the etoposide dimethoxyphenol ring may be responsible for the formation of single-strand breaks. Double-strand breaks were unrepaired 20 h after the change of the incubation medium. The number of double-strand breaks and a proportion of apoptotic cells did not exhibit any dependence on VP-16 concentration and/or duration of cell exposure to this agent. We suggest that the cytotoxic effect of VP-16 on unstimulated lymphocytes is mediated by a topoisomerase II isoform, topoisomerase II-beta, which is localized in the nucleolus and is not related to the cell cycle.     

A facile method to study DNA synthesis in the cyanobacteriumSynechocystis PCC 6803

For the efficient study of replication of DNA, the cyanobacteriumSynechocystis PCC 6803 was first permeabilized by eitherl--lysophosphatidylcholine (LPC) or lysozyme-EDTA treatment. Permeability of the treated cells was evidenced by the incorporation of exogenously added³²P-TTP into DNA. In cells permeabilized by treatment with either method, the³²P-TTP incorporation at 30°C was appreciably higher than that in untreated control cells and increased with time for about 4 h. In addition, treated cells became permeable to proteins such as DNase I and micrococcal nuclease, which entered cells and degraded the newly synthesized DNA. Lysozyme/EDTA-treated cells not only incorporated³²P-TTP more efficiently than did LPC-permeabilized cells, but were capable of uptake and synthesis of exogenously supplied cyanobacterial plasmids isolated fromSynechocystis 6803. This capacity of lysozyme/EDTA-treatedSynechocystis to catalyze replication of exogenous DNA will allow the facile identification of DNA replication origins and their related regulatory sequences.     

There is substantial nuclear and cellular disintegration before detectable phosphatidylserine exposure during the camptothecin-induced apoptosis of HL-60 cells

BACKGROUND: An early sign of apoptosis in many cells is the appearance of phosphatidylserine (PS) on the outside of the plasma membrane, whilst the cells still retain the ability to exclude DNA-binding molecules such as propidium iodide and 7-aminoactinomycin D (7-AAD). The protein annexin V binds preferentially to PS and has often been used to monitor the early phase of apoptosis. There have been some conflicting results concerning whether annexin V binds to camptothecin (CAM)-treated HL-60 cells, a commonly used model for apoptosis. We investigated the effects of culturing HL-60 cells for up to 8 h with a range of CAM concentrations. METHODS: We used flow cytometry to measure cellular light scatter, annexin V-FITC binding, and 7-AAD uptake, and DNA content after fixation and permeabilization. We also used microscopy to examine the morphology of cells (both unsorted and sorted according to their light scatter) after cytocentrifugation. RESULTS: We found that CAM caused the rapid appearance of low light scatter apoptotic bodies. Even among cells with "normal" light scatter, there was widespread DNA cleavage and nuclear fragmentation by 3 h. The percentage of apoptotic bodies peaked at about 4 h and it was only afterward that annexin V binding could be detected to both intact cells and to apoptotic bodies. When they first appeared, the intact annexin V+ cells had S-phase DNA content. CONCLUSIONS: During CAM-induced apoptosis of HL-60 cells, the external exposure of PS can either precede or follow DNA cleavage, which suggests that PS exposure is not always an indicator of early apoptosis.     

2-(4-Methylphenyl)-1,3-selenazol-4-one induces apoptosis by different mechanisms in SKOV3 and HL 60 cells

We examined the ability of the synthetic selenium compound, 2-(4-methylphenyl)-1,3-selenazol-4-one (hereafter designated 3a), to induce apoptosis in a human ovarian cancer cell line (SKOV3) and a human leukemia cell line (HL-60). Flow cytometry showed that 3a treatment induced apoptosis in both cell lines to degrees comparable to that of the positive control, paclitaxel. Apoptosis was measured by PS externalization, DNA fragmentation and decreased mitochondrial membrane potential (MMP). However, analysis of the mechanism of action revealed differences between the responses of the two cell lines. Treatment with 3a arrested the cell cycle and induced caspase-3 activation in HL-60 cells, but not in SKOV3 cells. In contrast, 3a treatment induced apoptosis through translocation of AIF, a novel pro-apoptotic protein, in SKOV3 cells, but not in HL-60 cells. Collectively, our data demonstrated that 3a induced apoptosis in both cell lines, but via different action mechanisms.