GP7 can induce apoptotic DNA fragmentation of human leukemia cells through caspase-3-dependent and -independent pathways

GP7 (4-[4"-(2",2",6",6"-tetramethyl-l"-piperidinyloxy)amino]-4'-demethyl epipodophyllotoxin), a new spin-labeled derivative of podophyllotoxin, is a promising anticancer drug of podophyllotoxin class. The primary effect of GP7 is the anticancer activity on transplanted mouse tumors and cultured tumor cells. However, its molecular mechanism of action is still obscure. In this study, we investigated the activity of GP7 to induce apoptosis in human leukemia HL-60 and Jurkat cells. Apoptosis was determined by detection of DNA fragmentation in agarose gel electrophoresis. GP7 induced apoptotic DNA fragmentation of HL-60 and Jurkat cells in time- and dose-dependent manner. We further investigated the activity of caspase-3 in GP7-induced apoptotic DNA fragmentation of HL-60 and Jurkat cells. GP7 also induced time- and dose-dependent caspase-3 activation in both cell lines, and the kinetics of caspase-3 activation induced by GP7 was well correlated with that of apoptotic DNA fragmentation. To determine the role of caspase-3 in GP7-induced apoptotic DNA fragmentation, we examined the effect of specific caspase-3 inhibitor, Ac-DEVD-CHO, on GP7-induced apoptotic DNA fragmentation. Ac-DEVD-CHO prevented GP7-induced caspase-3 activation in both HL-60 and Jurkat cells, however, it only inhibited GP7-induced apoptotic internucleosomal DNA fragmentation in HL-60 cells. We then employed L-carnitine to investigate the role of caspase-3 in GP7-induced apoptotic DNA fragmentation. L-carnitine treatment prevented GP7-induced caspase-3 activation in both cell lines in a dose-dependent manner. Similar to Ac-DEVD-CHO, L-carnitine only inhibited GP7-induced apoptotic internucleosomal DNA fragmentation in HL-60 cells. These findings suggest that GP7 exerts an anti-leukemic effect by both caspase-3-dependent and -independent apoptotic signaling pathways.     

Ectopic expression of Bcl-2 and Bcl-xL inhibits apoptosis induced by TNF-related apoptosis-inducing ligand (TRAIL) through suppression of caspases-8, 7, and 3 and BID cleavage in human acute myelogenous leukemia cell line HL-60.

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is one of the latest members of the TNF superfamily known to induce apoptosis in a wide variety of tumor cells. Some cell types, however, are quite resistant to TRAIL. We investigated the effect of ectopic expression of Bcl-2 and Bcl-xL on TRAIL-induced apoptosis in human acute myelogenous leukemia HL-60 cells. We found that HL-60 cells, which express TRAIL receptors (also called death receptor, DR) DR4, DR5, and Dc (decoy) R2, are highly sensitive to TRAIL-induced cytotoxicity. Greater than 90% killing occurred within 24 h of TRAIL treatment. The expression of Bcl-2 and Bcl-xL, however, completely abolished the TRAIL-induced cytotoxic effects. Treatment of HL-60 cells with TRAIL induced caspase-8 activation within 2-4 h, but no activation could be seen in Bcl-2-expressing or Bcl-xL-expressing cells. TRAIL also induced cleavage of BID, which was also abolished by Bcl-2 and Bcl-xL. Similarly, TRAIL activated caspase-3 and caspase-7 in control cells but not in cells expressing Bcl-2 or Bcl-xL. Cleavage of the caspase-3 substrate poly(ADP-ribose) polymerase (PARP), was abrogated by ectopic expression of Bcl-2 and Bcl-xL. Inhibition of caspases by the pan-caspase inhibitor, benzyloxycarbonyl-valine-alanine-aspartate-fluoromethylketone (zVAD-fmk) abolished the TRAIL-induced apoptosis. Overall, these results indicate that TRAIL-induced apoptosis involves activation of caspase-8, caspase-7, caspase-3, and BID cleavage, and Bcl-2 and Bcl-xL prevents TRAIL-induced apoptosis by abrogating caspase activation and BID cleavage.     

The Notch ligand, Delta-1, reduces TNF-alpha-induced growth suppression and apoptosis by decreasing activation of caspases in U937 cells

The Notch signaling pathway plays an important role in the regulation of self-renewal and differentiation of hematopoietic progenitors. Tumor necrosis factor (TNF)-alpha induces apoptosis through activation of caspase pathway. A monoblastic leukemia cell line, U937, undergoes apoptosis following stimulation with TNF-alpha. We found that Notch activation induced by a recombinant Notch ligand, Delta-1, reduced the TNF-alpha-induced growth suppression and apoptosis in U937 cells. As the molecular mechanism involved, we showed Delta-1 stimulation partially suppressed the sequential activation of caspase-8, caspase-3, and, PARP induced by TNF-alpha. The TNF-alpha-induced activation of c-Jun N-terminal kinase (JNK), p38, and NF-kappaB was not affected by Delta-1 stimulation. The cells needed to be exposed to Delta-1 prior to TNF-alpha stimulation to reduce the suppressive effect of TNF-alpha. Therefore, we thought that Delta-1 stimulation might reduce the expression of TNF-receptor (R) 1 and proteins to modulate the activation of caspases such as FLIP and XIAP. However, Delta-1 stimulation did not affect their expression. The precise mechanism by which Notch signaling suppresses caspase activation has yet to be determined. This is the first report to show the relationship between Notch activation and TNF-R1 signaling. The findings suggest possible mechanisms by which Notch activation supports cell survival.     

齐墩果酸诱导人白血病HL-60细胞凋亡及细胞周期阻滞

目的：探讨齐墩果酸诱导HL-60细胞凋亡作用及其对细胞周期的影响。方法：以HL-60细胞为研究对象，以不同剂量的齐墩果酸处理HL-60细胞12 h、24 h、48 h、72 h后，用MTT法观察HL-60细胞的生长抑制率；琼脂糖凝胶电泳测定DNA梯形条带；流式细胞仪分析HL-60细胞细胞周期的变化；同时用Western blotting 检测凋亡途径最终执行者caspase-3的表达。结果：齐墩果酸对HL-60细胞生长具有明显的抑制作用，其中80 μmol/L齐墩果酸作用48 h对HL-60细胞的抑制率达到50%以上，齐墩果酸诱导细胞凋亡呈明显的时间和剂量依赖性； HL-60经齐墩果酸处理48 h出现典型的DNA梯形条带；以80 μmol/L的齐墩果酸处理HL-60细胞12 h即可以使caspase-3的前体procaspase-3断裂为有活性的caspase-3；流式细胞技术检测结果表明HL-60细胞经齐墩果酸处理后细胞周期阻滞于G₁期，其中48 h和72 h分别达到63.24%和67.90%。结论：齐墩果酸可以诱导HL-60细胞凋亡，并使细胞阻滞于G₁期。     

达努塞替对HL-60细胞抗肿瘤作用机制的研究

目的:探讨丝氨酸/苏氨酸激酶抑制剂达努塞替对人急性髓细胞白血病(AML)细胞株HL-60的细胞周期阻滞、自噬和凋亡的影响。方法:用MTT法检测达努塞替对HL-60细胞的生长抑制作用;用流式细胞术检测相同时间不同浓度药物组与同一浓度不同时间组的细胞周期、细胞凋亡及细胞自噬;用Western blot方法检测细胞周期相关蛋白CDK1/CDC2、CDK2、cyclin B1、P21Waf1/Cip1、P27Kip1和P53,凋亡相关蛋白Bcl-x L、Bcl-2、Bax、PUMA、cleaved caspase-3及cleaved caspase-9以及自噬相关蛋白p-PI3K、PTEN、p-Akt、p-m TOR、Beclin 1、LC3-I和LC3-II的水平。用共聚焦显微镜检测同时间不同浓度药物组细胞的自噬情况。结果:达努塞替能明显抑制HL-60细胞的活力,诱导细胞周期G2/M期阻滞,可以通过线粒体caspase-3途径诱导细胞凋亡,同时可以通过抑制PI3K/Akt/m TOR信号通路诱导细胞自噬。结论:达努塞替可通过抑制作为染色体伴侣蛋白且在有丝分裂中调控染色质复制与分离的极光激酶A/B有效抑制HL-60细胞生长,引起细胞周期阻滞、凋亡和自噬发生,可能是AML临床治疗具有前景的抗肿瘤靶点。     

SU11248对白血病细胞HL-60增殖及凋亡作用的实验研究

目的:探讨新型抗肿瘤药物苹果酸舒尼替尼(SU11248)对白血病细胞HL-60的生物学效应的影响及其作用机制。方法:应用MTT法检测SU11248对HL-60细胞增殖能力的影响;用AnnexinV/PI双染流式细胞术检测细胞凋亡;用流式细胞技术分析细胞的DNA倍体及细胞周期变化;用凝胶电泳分析DNA片段化;以Western blot法检测2.0μg/ml SU11248作用HL-60后bcl-2、bax、caspase-3蛋白水平的变化。结果:SU11248可明显抑制HL-60细胞增殖(P<0.05),呈剂量和时间依赖性,半数抑制浓度(IC50)约为2.00μg/ml。SU11248可促进细胞凋亡,并呈剂量依赖性;能将HL-60细胞阻滞于G0/G1期,并呈时间依赖性;诱导HL-60细胞呈典型的DNA梯带;SU11248作用后bcl-2蛋白表达随时间依赖性降低,caspase-3蛋白表达升高,bax蛋白表达无明显变化。结论:SU11248能抑制HL-60细胞增殖,诱导其凋亡,调节bcl-2家族蛋白的表达,并裂解caspase-3是其可能作用机制之一。     

In vitro cytotoxicity of Mokko lactone in human leukemia HL-60 cells: induction of apoptotic cell death by mitochondrial membrane potential collapse

We studied the effect of mokko lactone (ML) isolated from the roots of Saussurea lappa (Compositae), a plant that is used for medicinal purposes in Korea, on the induction of apoptosis in human leukemia HL-60 cells. ML was cytotoxic to HL-60 cells, and this cytotoxic effect of ML appears to be attributable to its induction of apoptotic cell death, as ML induced nuclear morphologic changes and internucleosomal DNA fragmentation and increased the proportion of Annexin V-positive cells and the activity of caspase-3. Further studies revealed that the induction of apoptosis by ML was associated with the loss of mitochondrial membrane potential. Collectively, our results suggest that apoptosis induced by ML in HL-60 cells was executed by a collapse of mitochondrial membrane potential followed by the activation of caspase-3. This is the first report on the mechanism of apoptosis-inducing effect of ML.     

In Vitro Cytotoxicity of Mokko Lactone in Human Leukemia HL-60 Cells: Induction of Apoptotic Cell Death by Mitochondrial Membrane Potential Collapse

We studied the effect of mokko lactone (ML) isolated from the roots of Saussurea lappa (Compositae), a plant that is used for medicinal purposes in Korea, on the induction of apoptosis in human leukemia HL-60 cells. ML was cytotoxic to HL-60 cells, and this cytotoxic effect of ML appears to be attributable to its induction of apoptotic cell death, as ML induced nuclear morphologic changes and internucleosomal DNA fragmentation and increased the proportion of Annexin V-positive cells and the activity of caspase-3. Further studies revealed that the induction of apoptosis by ML was associated with the loss of mitochondrial membrane potential. Collectively, our results suggest that apoptosis induced by ML in HL-60 cells was executed by a collapse of mitochondrial membrane potential followed by the activation of caspase-3. This is the first report on the mechanism of apoptosis-inducing effect of ML.     

Antiapoptotic action of focal adhesion kinase (FAK) against ionizing radiation

Focal adhesion kinase (FAK) has an antiapoptotic role in anchorage-dependent cells via an unknown mechanism. To elucidate the role of FAK in the antiapoptosis, we have demonstrated that FAK-overexpressed (HL-60/FAK) cells have marked resistance against various apoptotic stimuli. That is, HL-60/FAK cells were highly resistant to hydrogen peroxide or etoposide-induced apoptosis compared with the vector-transfected cells. In this study, we demonstrated that HL-60/FAK cells were highly resistant to ionizing radiation (IR)-induced apoptosis. IR at 10-40 Gy induced significant DNA fragmentation, activation of caspase-3 and -8, the processing of a proapoptotic BID, and mitochondrial release of cytochrome c in the parental or HL-60/Vect cells, whereas no significant DNA fragmentation or no other concurring events were observed in the HL-60/FAK cells. Of note is that, in the HL-60/FAK cells, phosphatidylinositol 3'-kinase-Akt survival pathway was activated, accompanied with significant induction of inhibitor-of-apoptosis proteins (cIAP-2, XIAP). Finally, constructs of FAK mutants revealed that the central kinase domain (K454), autophosphorylation site (Y397), as well as focal adhesion target regions (Y925), were prerequisite for the FAK function. These results indicated that mitochondria pathway is required for IR-induced apoptosis, and FAK overexpression prevents this pathway, thus rendering antiapoptotic states.     

高三尖杉酯碱对HL60细胞凋亡的影响及机制的研究

目的:研究高三尖杉酯碱对HL60细胞凋亡的影响及其机制。方法:运用高三尖杉酯碱作用HL60细胞后撤药实验筛选其诱导HL60细胞凋亡启动时相,流式细胞和免疫组化技术检测高三尖杉酯碱诱导HL60细胞凋亡启动时相凋亡信号分子Bcl-2、Bax、Fas/FasL、caspase-3、ERK2和p38的表达状况。结果:在高三尖杉酯碱诱导HL60细胞凋亡启动时相,Bcl-2表达降低,Bax表达增高,Bcl-2/Bax比值降低,ERK2表达减低,p38表达增加,caspase-3表达增加,Fas/FasL分子的表达无显著变化。结论:Bcl-2、Bax、MAPK途径和caspase-3参与高三尖杉酯碱启动HL60细胞凋亡的信号转导。     

Apoptosis triggered by phagocytosis-related oxidative stress through FLIPS down-regulation and JNK activation

Tumor necrosis factor-alpha (TNF-alpha)-activated neutrophils phagocytose and eliminate bacteria by using such oxidants as hydrogen peroxide (H(2)O(2)) and hypochlorous acid (HOCl), which is produced from H(2)O(2) by myeloperoxidase (MPO). Thereafter, neutrophils eventually undergo apoptosis to prevent excessive inflammation. However, it is unclear how this process is regulated. Here, we show that cotreatment of TNF-alpha-resistant neutrophilic HL-60 cells with taurine chloramine (TauCl), a detoxified form of HOCl, and TNF-alpha renders them susceptible to apoptosis, mostly by preventing nuclear factor-kappaB (NF-kappaB) activation. Of several NF-kappaB target genes tested, FLICE inhibitory protein short form (FLIP(S)) was specifically down-regulated by TauCl. TNF-alpha/TauCl cotreatment-induced apoptosis was largely blocked by stable expression of FLIP(S). Cotreatment with TNF-alpha and H(2)O(2) promoted apoptotic signaling via MPO activation and subsequent attenuation of FLIP(S) expression. TNF-alpha priming with H(2)O(2) or bacteria caused MPO-dependent apoptosis in human neutrophils. However, FLIP(S) knock-down by siRNA did not affect the viability of cells treated with TNF-alpha, implying that TauCl may affect another pathway in TNF-alpha-driven apoptosis. Indeed, oxidization of thioredoxin-1 (Trx-1) by TauCl induced the activation of apoptosis signal-regulating kinase 1 (ASK1) and cJun N-terminal kinase (JNK), thereby triggering TNF-alpha-mediated apoptosis. Taken together, these results indicate that the antiapoptotic signaling induced by TNF-alpha via NF-kappaB activation can be altered to promote apoptosis via H(2)O(2)-MPO-mediated FLIP(S) down-regulation and JNK activation.     

Molecular mechanism of satratoxin-induced apoptosis in HL-60 cells: activation of caspase-8 and caspase-9 is involved in activation of caspase-3

Satratoxins have been recognized as potential immunomodulatory agents in outbreaks of building-related illness. Here we report that satratoxin G-treated human leukemia HL-60 cells underwent apoptosis through the action of caspase-3 which was activated by both caspase-8 and caspase-9. Western blot analysis of caspase-3 in the satratoxin G-treated cells apparently indicated the appearance of a catalytically active fragment of 17 kDa. Increased caspase-3 activity was also detected by using a fluorogenic substrate, DEVD-AMC. Next, exposure to satratoxin G led to cleavage of PARP from its native 116 kDa form to a 85 kDa product. Moreover, DFF-45/ICAD were cleaved into a 12.5 kDa fragment via satratoxin G treatment. Enzymic assay on IETD-AMC revealed that caspase-8 is strongly activated by exposure to satratoxin G while T-2 toxin (T-2) could not activate caspase-8 at an early stage of apoptosis. Furthermore, satratoxin G caused a release of cytochrome c from mitochondria into the cytosol and increased the activity of caspase-9 against LEHD-AMC. These findings indicate that satratoxin G-induced apoptosis involves activation of caspase-3 and DFF-40/CAD through both activation of caspase-8 and cytosolic accumulation of cytochrome c along with activation of caspase-9.     

Involvement of NF-kappaB and mitochondrial pathways in docetaxel-induced apoptosis of human oral squamous cell carcinoma

Apoptosis induced by docetaxel that interferes with microtubule polymerization dynamics and is used clinically to treat advanced cancers, has not been fully defined in squamous cell carcinoma. In this study, apoptotic events involved in docetaxel treatment were investigated. When the human oral squamous cell carcinoma cell line HSC-3 was exposed to docetaxel for 72 h, a dose-dependent effect was observed in apoptosis using the TUNEL method. We observed activation of caspase cascade including activities like caspase-3, -8, and -9. And the pan-caspase inhibitor z-VAD-fmk prevented apoptosis induced by docetaxel (0.1 microM), showing participation of caspases in this process. Since an antagonistic CD95-antibody (ZB4) exerted no effect on docetaxel-induced apoptosis, CD95/CD95L interaction was not involved in this pathway. The caspase-8-like activity was inhibited not only by IETD-fmk (caspase-8) but also by DEVD-fmk (caspase-3). The results indicate that the caspase-8-like activation occurred downstream of DEVDase. Docetaxel promoted the formation of reactive oxygen species (ROS) in mitochondria, and preincubation of cells with anti-oxidants such as N-acetyl cysteine and pyrrolidine dithiocarbamate, protected against apoptosis mediated by docetaxel. Furthermore, treatment with docetaxel elicited reduction of mitochondrial membrane potential, and release of cytochrome c to cytosol, after 48 h of treatment. We observed binding activity to NF-kappaB consensus site and interference with the mitochondrial function via NF-kappaB after docetaxel treatment. Preventing pro-apoptotic property of NF-kappaB inhibited docetaxel-induced apoptosis. Thus, these results suggest that, following the activation of NF-kappaB by docetaxel, apoptosis is elicited through a mitochondria-dependent pathway.     

CD8+ T cell apoptosis induced by Escherichia coli heat-labile enterotoxin B subunit occurs via a novel pathway involving NF-kappaB-dependent caspase activation

The B subunit of Escherichia coli heat-labile enterotoxin (EtxB) is a potent immunomodulatory molecule capable of treating and preventing autoimmune disease. These properties result from its ability to bind to glycolipid receptors, principally G(M1) ganglioside, and modulate immune cell function. EtxB receptor binding causes B cell activation, modulates monocyte cytokine secretion and triggers apoptosis of CD8+ T cells. These wide-ranging effects suggest that B subunit receptor interaction triggers signaling events affecting cellular differentiation. We have investigated the processes by which EtxB induces CD8+ T cell apoptosis. We show that receptor interaction by EtxB activates caspase-3 in CD8+ but not in CD4+ T cells. Inhibition of caspase-3 blocks the apoptotic process. EtxB induces the activation of NF-kappaB in both CD8+ and CD4+ T cells. The findings that (i) SN50, a peptide inhibitor of NF-kappaB nuclear translocation, prevents caspase-3 activation and subsequent apoptosis, and (ii) CD8+CD4- thymocytes from transgenic mice expressing a dominant-negative form of the IkappaBalpha protein were markedly less susceptible to EtxB-induced apoptosis than cells from wild-type mice, indicate that NF-kappaB is important in the induction of the apoptotic pathway. Further investigations revealed that while caspase-8 activity is detected concomitant to caspase-3, caspase-9 activation, following mitochondrial cytochrome c release, is detectable later on. These observations are consistent with death receptor-mediated signaling, however, experiments using lpr/lpr and p55 TNFR -/- mice rule out the involvement of Fas and the p55 TNF receptor, respectively. The data therefore indicate that EtxB-mediated apoptosis occurs via a novel pathway involving NF-kappaB.     

Baicalein induces apoptosis through ROS-mediated mitochondrial dysfunction pathway in HL-60 cells

Baicalein is one component of the dried root of Scutellaria Baicalensis Georgi. (Huang Qin) which is widely used in the traditional Chinese herbal medicine. In this study, we report that baicalein was able to induce apoptosis in human promyelocytic leukemia cells (HL-60), as characterized by poly-(ADP-ribose) polymerase (PARP) cleavage and DNA fragmentation. The efficacious induction of apoptosis was observed at 100 microM for 6 h. Mechanistic analysis demonstrated that baicalein induced the cleavage of Bid protein, cytochrome c release from mitochondria into cytosol, and activation of caspase-3, -8 and -9. Moreover, baicalein caused elevation of intracellular hydrogen peroxide level. Catalase could effectively block baicalein-induced DNA fragmentation. These data indicate that baicalein may trigger an apoptotic death program through reactive oxygen species (ROS)-mediated mitochondrial dysfunction pathway. The findings enhance our understanding of anticancer function of baicalein in herbal medicine.     

Nuclear factor-kappaB and caspases co-operatively regulate the activation and apoptosis of human macrophages

Accumulating evidence suggests that macrophages function as major effector cells in the pathological process of various human diseases. We examined here the role of nuclear factor-kappaB (NF-kappaB) and caspases in the regulation of activation and apoptosis of macrophages. Activation of the human monoblastic leukaemia cell line, U937, by phorbol 12-myristate 13-acetate (PMA) increased the expression of CD14/CD86, and cytokine production. PMA stimulation also increased the expression of both pro-caspase-8 and pro-caspase-3 in U937, but not apoptosis or intracellular caspase-3 activity. PMA also increased the expression of X-chromosome-linked inhibitor of apoptosis protein (XIAP) in U937, suggesting an inhibitory action for XIAP on the caspase cascade in PMA-stimulated U937. Electrophoretic mobility shift assay (EMSA) showed a significant increase of nuclear NF-kappaB activity in PMA-stimulated U937. When a potent NF-kappaB inhibitor, pyrrolidine dithiocarbamate (PDTC), was added to U937 cell culture in the presence of PMA, apoptosis was triggered by activation of caspase-3, which was induced by caspase-8 activation. XIAP expression was markedly suppressed in PMA-treated U937 in the presence of PDTC. The inhibitors of caspase-8 and caspase-3 mostly inhibited apoptosis of U937 treated with PMA in the presence of PDTC. Furthermore, a phenotype of U937 treated with PMA and PDTC in the presence of caspase inhibitor was almost identical to that of unstimulated U937. Our results suggest that the signalling pathways involved in the activation and apoptosis of human macrophages could be co-operatively regulated by the use of NF-kappaB and caspase inhibitors, thus enabling the control of macrophage function and number.