Apicidin, a histone deacetylase inhibitor, induces apoptosis and Fas/Fas ligand expression in human acute promyelocytic leukemia cells.

We previously reported that apicidin arrested human cancer cell growth through selective induction of p21(WAF1/Cip1). In this study, the apoptotic potential of apicidin and its mechanism in HL60 cells was investigated. Treatment of HL60 cells with apicidin caused a decrease in viable cell number in a dose-dependent manner and an increase in DNA fragmentation, nuclear morphological change, and apoptotic body formation, concomitant with progressive accumulation of hyperacetylated histone H4. In addition, apicidin converted the procaspase-3 form to catalytically active effector protease, resulting in subsequent cleavages of poly(ADP-ribose) polymerase and p21(WAF1/Cip1). Incubation of HL60 cells with z-DEVD-fmk, a caspase-3 inhibitor, almost completely abrogated apicidin-induced activation of caspase-3, DNA fragmentation, and cleavages of poly(ADP-ribose) polymerase and p21(WAF1/Cip1). Moreover, these effects were preceded by an increase in translocation of Bax into the mitochondria, resulting in the release of cytochrome c and cleavage of procaspase-9. The addition of cycloheximide greatly inhibited activation of caspase-3 by apicidin by interfering with cleavage of procaspase-3 and DNA fragmentation, suggesting that apicidin-induced apoptosis was dependent on de novo protein synthesis. Consistent with these results, apicidin transiently increased the expressions of both Fas and Fas ligand. Preincubation with NOK-1 monoclonal antibody, which prevents the Fas-Fas ligand interaction and is inhibitory to Fas signaling, interfered with apicidin-induced translocation of Bax, cytochrome c release, cleavage of procaspase-3, and DNA fragmentation. Taken together, the results suggest that apicidin might induce apoptosis through selective induction of Fas/Fas ligand, resulting in the release of cytochrome c from the mitochondria to the cytosol and subsequent activation of caspase-9 and caspase-3.     

Cleavage of automodified poly(ADP-ribose) polymerase during apoptosis. Evidence for involvement of caspase-7.

The abundant nuclear enzyme poly(ADP-ribose) polymerase (PARP) synthesizes poly(ADP-ribose) in response to DNA strand breaks. During almost all forms of apoptosis, PARP is cleaved by caspases, suggesting the crucial role of its inactivation. A few studies have also reported a stimulation of PARP during apoptosis. However, the role of PARP stimulation and cleavage during this cell death process remains poorly understood. Here, we measured the stimulation of endogenous poly(ADP-ribose) synthesis during VP-16-induced apoptosis in HL60 cells and found that PARP was cleaved by caspases at the time of its poly(ADP-ribosyl)ation. In vitro experiments showed that PARP cleavage by caspase-7, but not by caspase-3, was stimulated by its automodification by long and branched poly(ADP-ribose). Consistently, caspase-7 exhibited an affinity for poly(ADP-ribose), whereas caspase-3 did not. In addition, caspase-7 was activated and accumulated in the nucleus of HL60 cells in response to the VP-16 treatment. Furthermore, caspase-7 activation was concommitant with PARP cleavage in the caspase-3-deficient cell line MCF-7 in response to staurosporine treatment. These results strongly suggest that, in vivo, it is caspase-7 that is responsible for PARP cleavage and that poly(ADP-ribosyl)ation of PARP accelerates its proteolysis. Cleavage of the active form of caspase substrates could be a general feature of the apoptotic process, ensuring the rapid inactivation of stress signaling proteins.     

Mechanism of UV-Induced Apoptosis in Human Leukemia Cells: Roles of Ca/Mg-Dependent Endonuclease, Caspase-3, and Stress-Activated Protein Kinases

Ultraviolet light (UV) induced rapid apoptosis of U937 leukemia cells, concurrent with DNA fragmentation and cleavage of poly(ADP-ribose)polymerase (PARP) by activated caspase-3. Thein vitroreconstitution of intact HeLa S3 nuclei and apoptotic U937 cytosolic extract (CE) revealed that (i) Ca²⁺/Mg²⁺-dependent, Zn²⁺-sensitive endonuclease activated in the apoptotic CE induced DNA ladder in HeLa nuclei at pH 6.8–7.4, (ii) activated caspase-3 cleaved PARP in HeLa nuclei, and (iii) when the apoptotic CE was treated with the caspase-3 inhibitor (1 μM Ac-DEVD-CHO) or the caspase-1 inhibitor (10 μM Ac-YVAD-CHO), the former, but not the latter, caused a 50% inhibition of DNA fragmentation and the complete inhibition of PARP cleavage in HeLa nuclei. Similarly, Ac-DEVD-CHO (100 μM) inhibited apoptosis and DNA ladder by 50% and PARP cleavage completely in UV-irradiated U937 cells, but Ac-YVAD-CHO (100 μM) did not. Thus, UV-induced apoptosis of U937 cells involves the Ca²⁺/Mg²⁺-dependent endonuclease pathway and the caspase-3–PARP cleavage–Ca²⁺/Mg²⁺-dependent endonuclease pathway. The former pathway produced directly 50% of apoptotic DNA ladder, and the latter involved activated caspase-3 and PARP cleavage, followed by formation of the remaining 50% DNA ladder by the activated endonuclease. In UV-irradiated B-cell lines, further, p53-dependent increase of Bax resulted in a greater caspase-3 activation compared to its absence. However, UV-induced activation of JNK1 and p38 was not affected by the caspase-1 and -3 inhibitors in U937 cells, so that caspases-1 and -3 do not function upstream of JNK1 and p38.     

Oleanolic Acid Induces Apoptosis in Human Leukemia Cells through Caspase Activation and Poly（ADP-ribose） Polymerase Cleavage

It has been shown that Fructus Ligustri Lucidi （FLL）, a promising traditional Chinese medicine, can inhibit the growth of tumors. However, the effective component and molecular mechanism of FLL act to inhibit tumor proliferation are unclear. In this study, we demonstrated that oleanolic acid （OA）, a principal chemical component of FLL, inhibited the proliferation of human leukemia HL60 cells in culture. MTT assay showed that treatment of HL60 cells with FLL crude extracts or OA dramatically blocked the growth of target tumor cell in a time- and dose-dependent manner. Morphological changes of the nuclei and DNA fragmentation showed that apoptotic cell death occurred in the HL60 cells after treating with FLL extracts （20 mg/ml） or OA （3.65×10^-2 mg/ml）. Furthermore, flow cytometry assay showed that treatment of HL60 cells with FLL or OA caused an increased accumulation of G1 and sub-G1 subpopulations. Western blot analysis showed that caspase-9 and caspase-3 were activated, accompanied by the cleavage of poly （ADP-ribose） polymerase （PARP） in the target cells during FLL- or OA-induced apoptosis, These results suggest that OA acts as the effective component of FLL by exerting its cytotoxicity towards target tumor cells through activation of caspases and cleavage of PARP.     

Arsenic trioxide induces apoptosis of myeloid leukemia cells by activation of caspases

The primary objective of this study was to determine whether caspases are involved in arsenic trioxide(ATO)-induced apoptosis of human myeloid leukemia cells. A secondary objective was to determine whether apoptosis induced by ATO compared with VP-16 is differentially affected by an activator of protein kinase C (PKC), phorbol 12-myristate 13-acetate (PMA), which has been reported to inhibit apoptosis induced by some chemotherapeutic agents. NB4 and HL60 cells were incubated with ATO in the presence and absence of the caspase protease inhibitors Z-VAD.fmk or Y-VAD. cho. Apoptosis was assessed by morphology, DNA laddering and flow cytometry. Poly (ADP-ribose) polymerase (PARP) cleavage was used as a marker for the activation of caspases. PARP cleavage occurred during ATO-induced apoptosis in both NB4 and HL60 cells. Z-VAD.fmk, a broad-spectrum inhibtor, could block ATO-induced apoptosis and PARP cleavage, whilst Y-VAD. cho, a selective inhibitor of caspase 1, had no such effect. PMA pre-incubation for up to 8 hours under conditions known to activate PKC had no effect on either ATO- or VP-16-induced apoptosis. We conclude that in cultured myeloid leukemia cells ATO-induced apoptosis is executed by caspases from the distal, PARP-cleaving part of the activation cascade and that PKC activation has no effect on apoptosis induced by either ATO or VP-16 in these cells.     

Apoptosis induction by T-2 toxin: activation of caspase-9, caspase-3, and DFF-40/CAD through cytosolic release of cytochrome c in HL-60 cells

The molecules participating in apoptosis induced by T-2 toxin in human leukemia HL-60 cells were investigated. The rank order of the potency of trichothecene mycotoxins to induce internucleosomal DNA fragmentation was found to be T-2, satratoxin G, roridin A > diacetoxyscirpenol > baccharin B-5 > nivalenol, deoxynivalenol, 3-acetyldeoxynivalenol, fusarenon-X, baccharin B-4=vehicle control. Western blot analysis of caspase-3 in T-2-treated cells clearly indicated the appearance of its catalytically active fragment of 17-kDa. Increased caspase-3 activity was also detected by using a fluorogenic substrate, DEVD-AMC. Next, cells exposed to T-2 led to cleavage of PARP from its native 116-kDa form to the 85-kDa product. Moreover, DFF-45/ICAD were cleaved to give a 12.5-kDa fragment via T-2 treatment. T-2 caused the release of cytochrome c from mitochondria into the cytosol. Increased enzymic activity of caspase-9 on LEHD-AMC was shown. These data indicate that T-2-induced apoptosis involves activation of caspase-3 and DFF-40/CAD through cytosolic accumulation of cytochrome c along with caspase-9 activation.     

Photodynamic therapy induces caspase-3 activation in HL-60 cells

Caspases have been shown to play a crucial role in apoptosis induced by various deleterious and physiologic stimuli. In this study, we show for the first time that photodynamic therapy (PDT), using benzoporphyrin derivative monoacid ring A (BPD-MA, verteporfin) as the photosensitizer, induces the complete cleavage and subsequent activation of caspase-3 (CPP32/Yama/Apopain) but not caspase-1 (ICE) in human promyelocytic leukemia HL-60 cells. Poly(ADP-ribose) polymerase (PARP) and the catalytic subunit of DNA dependent protein kinase (DNA PK(CS)) were cleaved within 60 min of light activation of BPD-MA. The general caspase inhibitor Z-Asp-2,6 dichlorobenzoyloxymethylketone (Z-Asp-DCB) blocked PARP cleavage while the serine protease inhibitors 3,4-dichloroisocoumarin (DCI) and N-tosyl-lysyl chloromethyl ketone (TLCK) blocked the cleavage of caspase-3 suggesting that they act upstream of caspase-3 activation. All three inhibitors were able to block DNA fragmentation that was induced by treatment with BPD-MA followed by light application. These studies demonstrate that protease activity, particularly that of caspase-3, is triggered in HL-60 cells treated with lethal levels of BPD-MA and visible light.     

Involvement of caspase-3 activation in squamocin-induced apoptosis in leukemia cell line HL-60

Annonaceous acetogenins have potent antitumor effect in vitro and in vivo. Squamocin is one of the annonaceous acetogenins and has been reported to have antiproliferative effect on cancer cells. Our results from this study showed that squamocin inhibited proliferation of HL-60 cells with IC50 value of 0.17 microg/ml and induced apoptosis of HL-60 cells. Investigation of the mechanism of squamocin-induced apoptosis revealed that treatment of HL-60 cells with squamocin resulted in extensive nuclear condensation. DNA fragmentation, cleavage of the death substrate poly (ADP-ribose) polymerase (PARP) and induction of caspase-3 activity. Pretreatment of HL-60 cells with caspase-3 specific inhibitor DEVD-CHO prevented squamocin-induced DNA fragmentation, PARP cleavage and cell death. The expression levels of protein bcl-2, bax have no change in response to squamocin treatment in HL-60 cells, whereas stress-activated protein kinase (SAPK/JNK) was activated after treatment with squamocin in HL-60 cells. These results suggest that apoptosis of HL-60 cells induced by squamocin requires caspase-3 activation and is related to SAPK activation.     

A Novel Compound,L34, Induced Apoptosis in Human Gastric Cancer Cells

Selectively apoptosis-targeting compounds in gastrointestinal cancers attract broad interest. Here, we investigated a synthetic sulfonamide, 4-bromo-N-(5-ethyl-5H-pyrido[4,3-b]indol-8-yl)benzenesulfonamide (L34). It showed high activity against gastric cancer cells SGC-7901, causing apoptosis, which was associated with downregulation of caspase-3 and XIAP, upegulation of cleaved caspase-3, and cleavage of PARP. Hence, L34 might be a potent chemotherapeutic agent against human gastric cancer.     

Granzyme B activates procaspase-3 which signals a mitochondrial amplification loop for maximal apoptosis

Granzyme B (GrB), acting similar to an apical caspase, efficiently activates a proteolytic cascade after intracellular delivery by perforin. Studies here were designed to learn whether the physiologic effector, GrB-serglycin, initiates apoptosis primarily through caspase-3 or through BH3-only proteins with subsequent mitochondrial permeabilization and apoptosis. Using four separate cell lines that were either genetically lacking the zymogen or rendered deficient in active caspase-3, we measured apoptotic indices within whole cells (active caspase-3, mitochondrial depolarization [DeltaPsim] and TUNEL). Adhering to these conditions, the following were observed in targets after GrB delivery: (a) procaspase-3-deficient cells fail to display a reduced DeltaPsim and DNA fragmentation; (b) Bax/Bak is required for optimal DeltaPsim reduction, caspase-3 activation, and DNA fragmentation, whereas BID cleavage is undetected by immunoblot; (c) Bcl-2 inhibits GrB-mediated apoptosis (reduced DeltaPsim and TUNEL reactivity) by blocking oligomerization of caspase-3; and (d) in procaspase-3-deficient cells a mitochondrial-independent pathway was identified which involved procaspase-7 activation, PARP cleavage, and nuclear condensation. The data therefore support the existence of a fully implemented apoptotic pathway initiated by GrB, propagated by caspase-3, and perpetuated by a mitochondrial amplification loop but also emphasize the presence of an ancillary caspase-dependent, mitochondria-independent pathway.     

7-Hydroxystaurosporine (UCN-01) Induces Apoptosis in Human Colon Carcinoma and Leukemia Cells Independently of p53

7-hydroxystaurosporine (UCN-01) is a more selective protein kinase C inhibitor than staurosporine. UCN-01 exhibits antitumor activity in experimental tumor models and is presently in clinical trials. Our study reveals that human myeloblastic leukemia HL60 and K562 and colon carcinoma HT29 cells undergo internucleosomal DNA fragmentation and morphological changes characteristic of apoptosis after UCN-01 treatment. These three cell lines lack functional p53, and K562 and HT29 cells are usually resistant to apoptosis. DNA fragmentation in HT29 and K562 cells occurred after 1 day of treatment while it took less than 4 h in HL60 cells. Cycloheximide prevented UCN-01-induced DNA fragmentation in HT-29 cells, but not in HL60 and K562 cells, suggesting that macromolecular synthesis is selectively required for apoptotic DNA fragmentation in HT29 cells. UCN-01-induced DNA fragmentation was preceded by activation of cyclin B1/cdc2 kinase. Further studies in HL60 cells showed that UCN-01-induced apoptosis was associated with degradation of CPP32, PARP, and lamin B and that the inhibitor of caspases (ICE/CED-3 cysteine proteases), Z-VAD-FMK, and the serine protease inhibitor, DCI, protected HL60 cells from UCN-01-induced DNA fragmentation. However, only DCI and TPCK, but not Z-VAD-FMK, inhibited DNA fragmentation in the HL60 cell-free system, suggesting that serine protease(s) may play a role in the execution phase of apoptosis in HL60 cells treated with UCN-01. Z-VAD-FMK and DCI also inhibited apoptosis in HT29 cells. These data demonstrate that the protein kinase C inhibitor and antitumor agent, UCN-01 is a potent apoptosis inducer in cell lines that are usually resistant to apoptosis and lack p53 and that caspases and probably serine proteases are activated during UCN-01-induced apoptosis.     

Apoptosis induced by protein phosphatase 2A (PP2A) inhibition in T leukemia cells is negatively regulated by PP2A-associated p38 mitogen-activated protein kinase

Serine/threonine phosphatase regulation of phosphorylation-mediated intracellular signaling controls a number of important processes in mammalian cells. In this study, we show that constitutively active protein phosphatase 2A (PP2A), which is a serine/threonine phosphatase, is essential for T leukemia cell survival. Jurkat and CCRF-CEM T leukemia cells treated with the PP2A-selective inhibitor okadaic acid (OA) showed a dose- and time-dependent induction of apoptosis, as indicated by loss of mitochondrial transmembrane potential (delta psi(m)), cleavage-induced activation of caspase-3, -8, and -9, and DNA fragmentation. In addition, caspase-8 or caspase-9 inhibition with z-IETD-fmk or z-LEHD-fmk, respectively, largely prevented OA-induced apoptosis. Although OA treatment did not affect constitutive Bcl-2 expression, overexpression of Bcl-2 prevented both OA-induced DNA fragmentation and dissipation of delta psi(m). Furthermore, inhibition of caspase-3, -8, or -9 partially protected against OA-induced loss of delta psi(m). In addition, caspase-9 and caspase-3 inhibition largely prevented procaspase-3 and procaspase-8 cleavage, respectively, while caspase-8 inhibition partially interfered with procaspase-9 cleavage in OA-treated T leukemia cells. Thus, PP2A inhibition triggered the intrinsic pathway of apoptosis, which was enhanced by a mitochondrial feedback amplification loop. PP2A has also been implicated in the regulation of p38 mitogen-activated protein kinase (MAPK). Co-immunoprecipitation analysis revealed a physical association between the catalytic subunit of PP2A and p38 MAPK in T leukemia cells. Moreover, OA treatment caused p38 MAPK to be phosphorylated in a dose- and time-dependent fashion, indicating that PP2A prevented p38 MAPK activation. Although p38 MAPK activation usually promotes apoptosis, pharmacologic inhibition of p38 MAPK exacerbated OA-induced DNA fragmentation and loss of delta psi(m) in T leukemia cells, suggesting that, in this instance, the p38 MAPK signaling pathway promoted cell survival. Collectively, these findings indicate that PP2A and p38 MAPK have coordinate effects on signaling pathways that regulate the survival of T leukemia cells.     

A novel compound, L34, induced apoptosis in human gastric cancer cells

Selectively apoptosis-targeting compounds in gastrointestinal cancers attract broad interest. Here, we investigated a synthetic sulfonamide, 4-bromo-N-(5-ethyl-5H-pyrido[4,3-b]indol-8-yl)benzenesulfonamide (L34). It showed high activity against gastric cancer cells SGC-7901, causing apoptosis, which was associated with downregulation of caspase-3 and XIAP, upegulation of cleaved caspase-3, and cleavage of PARP. Hence, L34 might be a potent chemotherapeutic agent against human gastric cancer.     

p53-Independent caspase-mediated apoptosis in human leukaemic cells is induced by a DNA minor groove binder with antineoplastic activity

Treatment of HL60 and Jurkat leukaemic cell lines, both not expressing p53, with the new non-covalent DNA minor groove binder -bromoacryloyl-distamycin (PNU 151807), induces apoptosis as shown either morphologically or by DNA laddering formation. We evaluated the p53-independent mechanisms of activation of apoptosis in these cell systems, by determining the levels of different caspases at different times after treatment with PNU 151807. Through Western blotting analysis we could measure the cleavage of the 110 Kd form of PARP in both HL60 and Jurkat cells and correspondingly the activation of CPP32-caspase 3. The levels of caspase-1 did not change at any time after drug treatment. By using the tetrapeptidic sequence recognized by caspase-3 (DEVD-AMC) or by caspase-1 (YVAD-AMC) linked to fluorogenic substrate, we also demonstrated that only the DEVD sequence was recognized and cleaved after drug treatment, while no significant changes were found for YVAD peptides. PNU 151807-induced DNA fragmentation and DEVD-cleavage were both inhibited by concomitant treatment with the specific inhibitor DEVD-CHO, but not by YVAD-CHO, clearly demonstrating the direct activation of caspase-3-like caspases in the induction of programmed cell death in these cell lines after minor groove binder exposure.     

<Emphasis Type="Italic">N,N</Emphasis>-Dimethyl phytosphingosine sensitizes HL-60/MX2, a multidrug-resistant variant of HL-60 cells,to doxorubicin-induced cytotoxicity through ROS-mediated release of cytochrome <Emphasis Type="Italic">c</Emphasis> and AIF

Doxorubicin (Dox) is widely used to treat a variety of tumors. However, resistance to this drug is common, making successful treatment more difficult. Previously, we introduced a novel phytosphingosine derivative, N,N-dimethyl phytosphingosine (DMPS), as a potent anticancer therapeutic agent in human leukemia cells. This study was performed to investigate whether DMPS can sensitize HL-60/MX2, a multidrug-resistant variant of HL-60, to Dox-induced apoptosis. Low concentrations of DMPS sensitized HL-60/MX2 cells to Dox-induced apoptosis. Combined Dox + DMPS treatment-induced apoptosis was accompanied by the activation of caspase-8 and caspase-3 as well as PARP cleavage. Cytochrome c and AIF release were also observed in Dox + DMPS-treated HL60/MX2 cells. Pretreatment with z-VAD-fmk markedly prevented caspase-3 activation and moderately suppressed apoptosis, suggesting that Dox + DMPS-induced apoptosis is somewhat (not completely) dependent on caspase. Cytochrome c and AIF release were not affected by pretreatment with z-VAD-fmk. The ROS scavenger NAC efficiently suppressed not only ROS generation, but also caspase-3-mediated PARP cleavage, apoptosis, and release of cytochrome c and AIF, indicating a role of ROS in combined Dox + DMPS treatment-induced apoptotic death signaling. Taken together, these observations suggest that DMPS may be used as a therapeutic agent for overcoming drug-resistance in cancer cells by enhancing drug-induced apoptosis.     

In vivo and in vitro activation of caspase-8 and -3 associated with Helicobacter pylori infection

In vivo and in vitro studies have shown an increase in apoptosis in gastric epithelial cells in persons infected with Helicobacter pylori. H. pylori-induced activation of caspase-8 and -3 was evaluated using a human gastric adenocarcinoma cell line (AGS) and gastric tissue from humans and monkeys colonized with H. pylori. The enzymatic activity of caspase-8 was detected only in AGS cells exposed to H. pylori up to 24 h. The active form of caspase-8 was present by Western blot after exposure to H. pylori for 3 h and persisted through 24 h. Caspase-3 activity was present in AGS cells exposed to H. pylori for 3 h, reaching a maximum after 24 h (a sevenfold increase in activity). Caspase-8-mediated cleavage of procaspase-3 generated a 20-kDa band (indicative of the presence of active caspase-3) present only in AGS cells exposed to H. pylori. Active caspase-3 staining was markedly increased in gastric mucosa from infected persons and animals, compared to uninfected controls by immunohistochemistry. Stimulation of downstream events leading to apoptosis, such as the cleavage of PARP (poly adenosine-diphosphate-ribose polymerase) and DFF45 (DNA fragmentation factor 45) as a result of activation of caspase-3, was evaluated. PARP was cleaved, resulting in the presence of both an 89- and a 24-kDa band along with DFF45, resulting in the presence of 10- and 12-kDa bands only in gastric cells exposed to H. pylori. Our data show that H. pylori stimulates the activation of caspases and downstream mediators of caspase-induced apoptosis. This suggests that H. pylori-induced apoptosis is mediated through caspase pathways, which include the activation of caspase-8 and subsequent cleavage and activation of caspase-3. This is consistent with caspase-3 activation that was found in the gastric mucosa of humans and monkeys infected with H. pylori.     

Haplophytin-A induces caspase-8-mediated apoptosis via the formation of death-inducing signaling complex in human promyelocytic leukemia HL-60 cells

Haplophytin-A (10-methoxy-2,2-dimethyl-2,6-dihydro-pyrano[3,2-c]quinolin-5-one), a novel quinoline alkaloid, was isolated from the Haplophyllum acutifolium. In this study, we investigated the effect of haplophytin-A on the apoptotic activity and the molecular mechanism of action in human promyelocytic leukemia HL-60 cells. Treatment with haplophytin-A (50 μM) induced classical features of apoptosis, such as, DNA fragmentation, DNA ladder formation, and the externalization of annexin-V-targeted phosphatidylserine residues in HL-60 cells. In addition, haplophytin-A triggered the activations of caspase-8, -9, and -3, and the cleavage of poly (ADP-ribose) polymerase (PARP) in HL-60 cells. In addition, haplophytin-A caused the loss of mitochondrial membrane potential (ΔΨ_m) and the release of cytochrome c and Smac/DIABLO to the cytosol, and modulated the expression levels of Bcl-2 family proteins. We further demonstrated that knockdown of caspase-8 using its siRNA inhibited the mitochondrial translocation of tBid, the activations of caspase-9 and caspase-3, and subsequent DNA fragmentation by haplophytin-A. Furthermore, haplophytin-A-induced the formation of death-inducing signaling complex (DISC) and then activated caspase-8 in HL-60 cells. During haplophytin-A-induced apoptosis, caspase-8-stimulated tBid provide a link between the death receptor-mediated extrinsic pathway and the mitochondria- mediated intrinsic pathway. Taken together, these results suggest that the novel compound haplophytin-A play therapeutical role for leukemia via the potent apoptotic activity through the extrinsic pathway, involving the intrinsic pathway.     

Loss of programmed cell death 4 induces apoptosis by promoting the translation of procaspase-3 mRNA

The programmed cell death 4 (Pdcd4), a translation inhibitor, plays an essential role in tumor suppression, but its role in apoptosis remains unclear. Here we show that Pdcd4 is a critical suppressor of apoptosis by inhibiting the translation of procaspase-3 mRNA. Pdcd4 protein decreased more rapidly through microRNA-mediated translational repression following apoptotic stimuli than did the activation of procaspase-3, cleavage of poly(ADP)ribose polymerase (PARP) by active caspase-3, and nuclear fragmentation. Strikingly, the loss of Pdcd4 by the specific RNA interference increased procaspase-3 expression, leading to its activation and PARP cleavage even without apoptotic stimuli, and sensitized the cells to apoptosis. Thus, our findings provide insight into a novel mechanism for Pdcd4 as a regulator of apoptosis.     

Caspase Activation Accompanying Cytochrome c Release from Mitochondria Is Possibly Involved in Nitric Oxide-Induced Neuronal Apoptosis in SH-SY5Y Cells

Abstract : It is well known that caspases are produced as proforms, which are proteolytically cleaved and activated during apoptosis or programmed cell death. We report here that caspases are activated during apoptosis by treatment with NOC18, a nitric oxide (NO) donor. Our present experiments have examined the way in which NO induces neuronal cell death, using a new type of NO donor that spontaneously releases only NO without enzymatic metabolism. NOC18 induced apoptosis in human neuroblastoma SH-SY5Y cells in a concentration-and time-dependent manner as estimated by DNA fragmentation assay, FACScan analysis, and nuclear morphology. Oxyhemoglobin, an NO trapper, suppressed NOC18-triggered DNA fragmentation, indicating that NO from NOC18 is a real activator in this study. Upon the induction of apoptosis, an increase in caspase-3-like protease activity, but not caspase-1, was observed. Procaspase-2 protein, an inactive form of caspase-2, decreased dramatically. In addition, NOC18 also resulted in poly (ADP-ribose) polymerase (PARP) cleavage, yielding an 85-kDa fragment typical of caspase activity. Oxyhemoglobin blocked the decrease of procaspase-2 and the cleavage of PARP by NOC18 in a concentration-dependent manner. Moreover, NO elicited the release of cytochrome c into the cytosol during apoptosis. These results suggest that both stimulation of caspase activity and cytochrome c release are partly involved in NO-induced neuronal apoptosis.