Alteration in the expression of early stage processing enzymes of N-glycan during myeloid and monocytoid differentiation of HL-60 cells

The expressions of the enzymes participating in the early stage of N-glycan processing, Golgi alpha-Mase-I, alpha-Mase-II and GnT-I, GnT-II, were studied before and after HL-60 cells were differentiated to myelocytes or monocytes induced by ATRA or PMA, respectively. It was found that alpha-Mase-I activity and GnT-I mRNA were decreased by both ATRA and PMA, while alpha-Mase-II and GnT-II were altered insignificantly. The down-regulation of alpha-Mase-I and GnT-I was cell specific, since ATRA up-regulated alpha-Mase-I and GnT-I in the H7721 hepatocarcinoma cell line. However, in H7721 cells, PMA also decreased alpha-Mase-I and GnT-I, and both ATRA and PMA also did not obviously change the expressions of alpha-Mase-II and GnT-II.

Beta-hydroxyisovalerylshikonin induces apoptosis in human leukemia cells by inhibiting the activity of a polo-like kinase 1 (PLK1)

beta-Hydroxyisovalerylshikonin (beta-HIVS), which was isolated from the plant, Lithospermum radix, induces apoptosis in various lines of human tumor cells. To identify genes involved in beta-HIVS-induced apoptotic process, we performed cDNA array analysis and found that beta-HIVS suppresses the expression of the gene for a polo-like kinase 1 (PLK1) that is involved in control of the cell cycle. When U937 and HL60 cells were treated with 10(-6) M beta-HIVS for 0.5 h, both the amount of PLK1 itself and the kinase activity of this enzyme were decreased. By contrast, Bcr-Abl-positive K562 cells were resistant to the induction of apoptosis by beta-HIVS and this compound did not suppress the kinase activity of PLK1 in these cells. However, simultaneous treatment of K562 cells with both beta-HIVS and STI571, which selectively inhibits the protein tyrosine kinase (PTK) activity of Bcr-Abl, strongly induced apoptosis. Moreover, beta-HIVS increased the inhibitory effect of STI571 on PTK activity. Treatment of K562 cells with antisense oligodeoxynucleotides (ODNs) specific for PLK1 sensitized these cells to the beta-HIVS-induced fragmentation of DNA. These results suggest that suppression of the activity of PLK1 via inhibition of tyrosine kinase activity by beta-HIVS might play a critical role in the induction of apoptosis.

Cyclic AMP induces activation of extracellular signal-regulated kinases in HL-60 cells: role in cAMP-induced differentiation

It is well known that elevated intracellular cAMP induces growth arrest and the differentiation of HL-60 cells to neutrophil-like cells. The present study was designed to assess the regulation of the extracellular signal-regulated kinase (ERK) pathway by cAMP and its association with differentiation in HL-60 cells. We found that 8-bromoadenosine-3',5'-cyclic-monophosphate (8Br-cAMP)-induced the activation of ERK and mitogen-activated protein kinase (MEK), but inhibited B-Raf kinase via a protein kinase A (PKA)-mediated mechanism. Prolonged exposure to 8Br-cAMP increased the phorbol 12-myristate 13-acetate (TPA)-stimulated superoxide generation and CD14 expression that characterize the differentiation phenotype, which was blocked by MEK-1 inhibitor. These data suggest that cAMP-induced ERK activation is essential for the differentiation of HL-60 cells, independently of B-Raf.

Induction of poly(ADP-ribose) polymerase-1 cleavage by antitumor triptycene bisquinones in wild-type and daunorubicin-resistant HL-60 cell lines

In contrast to their inactive parent compound triptycene (code name TT0), new synthetic analogs (TT code number) mimic the antitumor effects of the anthracycline quinone antibiotic daunorubicin (DAU) in the nM range in vitro but have the additional advantage of also blocking nucleoside transport and retaining their efficacy in multidrug-resistant (MDR) tumor cells. Since TT bisquinones may induce DNA fragmentation at 24 h by an active mechanism that requires RNA and protein syntheses and protease activities, the most cytotoxic of them, TT24, was tested for its ability to induce poly(ADP-ribose) polymerase-1 (PARP-1) cleavage, an early marker of apoptosis. PARP-1 cleavage starts at 2-3 h and is maximally induced at 6 h by 1.6 microM concentrations of TT24 and DAU in wild-type drug-sensitive HL-60-S cells. However, in MDR HL-60-RV cells, PARP-1 cleavage is still induced by 4 microM TT24 but not by 4-10 microM DAU. The magnitude of PARP-1 cleavage may increase with the number of quinoid rings in the triptych structure and, in contrast to TT0, all lead antitumor TT bisquinones share the ability to fully induce PARP-1 cleavage in HL-60-S cells. A 1 h pulse treatment is sufficient for TT24 and DAU to induce PARP-1 cleavage at 6 h. Since the abilities of TT24 and DAU to induce PARP-1 cleavage are inhibited by benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone but not by N-tosyl-L-phenylalanine chloromethyl ketone, caspase-mediated apoptosis may be involved in the mechanism by which these quinone antitumor drugs induce the proteolytic cleavage of PARP-1 at 6 h and the internucleosomal fragmentation of DNA at 24 h in the HL-60 tumor cell system.

Detection of activity of telomerase in tumor cells using fiber optical biosensors

Human telomerase plays an important role in the cancerogenesis as it is up-regulated in 80-90% of malignant tumors. Thus, it is considered as a potential cancer marker and relevant target in oncology. Its task is the extension of guanine-rich strands of the telomere using an intrinsic RNA as the template. In this paper we developed a new biosensoric assay based on total internal reflection fluorescence measuring the activity of the telomerase on sensor surface. Two alternatives to determine the telomeric activity are demonstrated without the use of amplifying steps as e.g. PCR. The enzymatic inclusion of FITC-labeled dUTPs should reveal the synthesis process in real-time indicating the elongation of a phosphothioate telomeric substrate (PS/TS)-modified primer. Additionally the elongated strand was detected by hybridization with a FITC-labeled complementary linear DNA probe. As the telomeric guanine-rich single-stranded DNA adopts intramolecular quadruplex structures, it was necessary for the hybridization to linearize the telomeric DNA by increasing the reaction temperature to 48 degrees C. The comparison of the telomerase activity using labeled and unlabeled nucleotides indicated the inhibition effect of the FITC-labeled nucleotides slowing down the synthesis rate of the enzyme. It is shown with the modified biosensor that the PS/TS primer binds the telomerase from the HL-60 cell lysates, effectively elongating the immobilized primer. Furthermore no more purification steps were required as all measurements were performed with crude cell extract.

Differential influence of etoposide on two caspase-2 mRNA isoforms in leukemic cells

Etoposide (VP-16) is an anticancer agent that induces apoptosis in human leukemic cell lines such as U937 and HL60. We performed RNase protection assays, with two distinct cRNA panels covering most of caspase and BCL-2-related genes, using total RNA from cell lines exposed to various concentrations of the drug. Our results show that VP-16 down-regulates expression of most surveyed genes with the noticeable exception of casp-2S mRNA that is up regulated whereas casp-2L mRNA is decreased. Since these mRNAs are produced by the alternative splicing of exon 9, we devised a reverse transcriptase-polymerase chain reaction method using primers from exons 8 and 10 to demonstrate that VP-16 stimulates the production of exon 9-containing sequences, irrespective of active transcription. However, this effect is specific of the 3'-end of the CASP-2 gene since no difference in the relative amounts of the 5'-end of the mRNA species is detected. Nevertheless, the level of full-length casp-2L mRNA together with that of procaspase-2L protein, which is pro-apoptotic, are decreased under VP-16 treatment, suggesting that an early cell response to treatment by cytotoxic agents is to down-regulate expression of selected pro-apoptotic proteins.

Detection of in situ activation of transglutaminase during apoptosis: correlation with the cell cycle phase by multiparameter flow and laser scanning cytometry

BACKGROUND

One of the hallmarks of apoptosis is activation of tissue transglutaminase (Tgase; also called transglutaminase type 2 [TGase 2]). Its activation causes cross-linking of cytoplasmic proteins, making them insoluble and presumably less immunogenic. Several biochemical and cytochemical methods to detect activity of TGase 2 exist, but none has been adapted for multiparameter flow or image cytometry.

METHODS

Apoptosis of HL-60 or U-937 leukemic cells was induced by camptothecin, tumor necrosis factor alpha, hyperthermia, or the cytotoxic RNase onconase. Two different approaches to detect TGase 2 activation were developed: (a) the unfixed cells were treated with 4',6'-diamidino-2-phenylindole, and sulforhodamine 101 in solutions of nonionic detergents; (b) the TGase 2 substrate fluoresceinated polyamine cadaverine (F-CDV) was administered into the cultures for several hours before cell harvesting. The cells were then fixed and their DNA counterstained with propidium. Cellular fluorescence was measured by flow or laser scanning cytometry.

RESULTS

(a) Exposure of nonapoptotic cells to detergents caused their full lysis, resulting in preparation of isolated nuclei devoid of cytoplasm. Conversely, the cross-linking of cytoplasmic protein by activated TGase 2 in apoptotic cells provided resistance to detergents: the nuclei or nuclear (chromatin) fragments of apoptotic cells remained attached to the cytoplasmic protein, embedded within the proteinaceous "shell." Such cells were identified by their high protein content: intensity of fluorescence after staining with the protein fluorochrome sulforhodamine 101 was markedly higher than that of isolated nuclei. (b) Activation of TGase 2 was also detected by virtue of intense cell labeling with fluoresceinated polyamine cadaverine. Interestingly, in many cells apoptosis progressed without evidence of activation of TGase 2, suggesting that this event may not be a prerequisite for completion of apoptosis.

CONCLUSIONS

Activation of TGase 2 can be detected simply by cell resistance to detergents or in situ reactivity with F-CDV. Both methods allow one to correlate activation of TGase 2 with the cell cycle position. However, because activation of TGase 2 is not always detected during apoptosis, the lack of the activation cannot be considered a marker of nonapoptotic cells. Hence, an apoptotic index based solely on TGase 2 activation may underestimate incidence of apoptosis.

Up-regulation of human deoxyribonuclease II gene expression during myelomonocytic differentiation of HL-60 and THP-1 cells

Several recent studies have suggested that intracellular deoxyribonuclease II (DNase II) is responsible for the degradation of DNA from apoptotic cells that are engulfed by macrophages. In this study, we studied DNase II expression during the phorbol 12-myristate-13-acetate (PMA)-induced differentiation of HL-60 and THP-1 cells. Basal levels of DNase II mRNA and protein were low, with expression being up-regulated approximately 15- and 7-fold, respectively, in HL-60 and THP-1 cells 72 h after PMA treatment. Nuclear run-on and luciferase reporter assays showed that transcription of DNase II gene was increased in PMA-treated cells. Together, these results demonstrate that DNase II gene transcription is increased during myelomonocytic differentiation, resulting in increased levels of mRNA and protein. This increase in DNase II levels in differentiated HL-60 and THP-1 cells suggests that it may play an important role in macrophages.

Differential regulation of telomerase activity by six telomerase subunits

Telomerase is a specialized reverse transcriptase responsible for synthesizing telomeric DNA at the ends of chromosomes. Six subunits composing the telomerase complex have been cloned: hTR (human telomerase RNA), TEP1 (telomerase-associated protein 1), hTERT (human telomerase reverse transcriptase), hsp90 (heat shock protein 90), p23, and dyskerin. In this study, we investigated the role of each the telomerase subunit on the activity of telomerase. Through down- or upregulation of telomerase, we found that only hTERT expression changed proportionally with the level of telomerase activity. The other components, TEP1, hTR, hsp90, p23, and dyskerin remained at high and unchanged levels throughout modulation. In vivo and in vitro experiments with antisense oligonucleotides against each telomerase component were also performed. Telomerase activity was decreased or abolished by antisense treatment. To correlate clinical sample status, four pairs of normal and malignant tissues from patients with oral cancer were examined. Except for the hTERT subunit, which showed differential expression in normal and cancer tissues, all other components were expressed in both normal and malignant tissues. We conclude that hTERT is a regulatable subunit, whereas the other components are expressed more constantly in cells. Although hTERT has a rate-limiting effect on enzyme activity, the other telomerase subunits (hTR, TEP1, hsp90, p23, dyskerin) participated in full enzyme activity. We hypothesize that once hTERT is expressed, all other telomerase subunits can be assembled to form a highly active holoenzyme.

Effects of Anaplasma phagocytophila on NADPH oxidase components in human neutrophils and HL-60 cells

The human granulocytic ehrlichiosis agent, Anaplasma phagocytophila, resides and multiplies exclusively in cytoplasmic vacuoles of granulocytes. A. phagocytophila rapidly inhibits the superoxide anion (O(2)(-)) generation by human neutrophils in response to various stimuli. To determine the inhibitory mechanism, the influence of A. phagocytophila on protein levels and localization of components of the NADPH oxidase were examined. A. phagocytophila decreased levels of p22(phox), but not gp91(phox), p47(phox), p67(phox), or P40(phox) reactive with each component-specific antibody in human peripheral blood neutrophils and HL-60 cells. Double immunofluorescence labeling revealed that p47(phox), p67(phox), Rac2, and p22(phox) did not colocalize with A. phagocytophila inclusions in neutrophils or HL-60 cells, and p22(phox) levels were also reduced. A. phagocytophila did not prevent either membrane translocation of cytoplasmic p47(phox) and p67(phox) or phosphorylation of p47(phox) upon stimulation by phorbol myristate acetate. The inhibitory signals for O(2)(-) generation was independent of several signals required for A. phagocytophila internalization. These results suggest that rapid alteration in p22(phox) induced by binding of A. phagocytophila to neutrophils is involved in the inhibition of O(2)(-) generation. Absence of colocalization of NADPH oxidase components with the inclusion further protects A. phagocytophila from oxidative damage.

Caspase inhibition and N6-benzyladenosine-induced apoptosis in HL-60 cells

As an extension of our recently published work (Mlejnek and Kuglík [2000] J. Cell. Biochem. 77:6-17), the role of caspases in N(6)-benzylaminopurine riboside (BAPR)-induced apotosis in HL-60 cells was evaluated in this study. Here, BAPR-induced apoptosis was accompanied by activation of caspase-3 and caspase-9. However, when these caspases were selectively inhibited, the progression of BAPR-induced apoptosis was not markedly affected. Besides that, activation of caspase-3 and caspase-9 was found to be rather late event in apoptotic process. These results suggested that other caspases might be critically implicated. Indeed, pan-specific caspase inhibitor, Z-VAD-FMK, completely prevented DNA cleavage and apoptotic bodies formation. However, Z-VAD-FMK failed to prevent cell death and it was incapable to fully counteract the main apoptotic hallmark-chromatin condensation. Finally, our data indicate that cellular decision between apoptosis and necrosis is made upon the availability of both caspase proteases and intracellular ATP.

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.

Decline of superoxide dismutase activity during antioxidant-induced apoptosis in HL-60 cells

Possible changes in Mn-containing superoxide dismutase (MnSOD) and Cu- and Zn-containing superoxide dismutase (CuZnSOD) activity during the apoptosis of human promyelocytic leukemia HL-60 cells, induced by three antioxidants, were investigated. Agarose gel electrophoresis of the DNA isolated from cells treated with sodium ascorbate, gallic acid or epigallocatechin gallate (EGCG) showed the internucleosomal DNA fragmentation, a biochemical hallmark of apoptosis. The optimum concentration for induction of DNA fragmentation was narrow and higher concentrations were rather inhibitory. Their effects were detected after 3 hours and reached a maximum level at 6 hours. Polyacrylamide gel electrophoresis and activity staining demonstrated that both MnSOD and CuZnSOD activities were significantly reduced at cytotoxic concentrations of all these compounds. Incubation of an intracellular MnSOD-enriched fraction with apoptosis-inducing concentrations of sodium ascorbate, gallic acid or EGCG did not significantly reduce the MnSOD activity, suggesting that their actions might be cell-mediated. These data suggest the mitochondrial dysfunction at the early stages of apoptosis.

Pharmacologic mitogen-activated protein/extracellular signal-regulated kinase kinase/mitogen-activated protein kinase inhibitors interact synergistically with STI571 to induce apoptosis in Bcr/Abl-expressing human leukemia cells

Interactions between the kinase inhibitor STI571 and pharmacological antagonists of the mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK)/mitogen-activated protein kinase (MAPK) cascade have been examined in human myeloid leukemia cells (K562 and LAMA 84) that express the Bcr-Abl kinase. Exposure of K562 cells to concentrations of STI571 that minimally induced apoptosis (e.g., approximately 200 nM) resulted in early suppression (i.e., at 6 h) of p42/44 MAPK phosphorylation followed at later intervals (i.e., > or =24 h) by a marked increase in p42/44 MAPK phosphorylation/activation. Coadministration of a nontoxic concentration of the MEK1/2 inhibitor PD184352 (5 microM) prevented STI571-mediated activation of p42/44 MAPK. Cells exposed to STI571 in combination with PD184352 for 48 h demonstrated a very dramatic increase in mitochondrial dysfunction (e.g., loss of DeltaPsim and cytosolic cytochrome c release) associated with procaspase-3 activation, poly(ADP-ribose) polymerase cleavage, and the appearance of the characteristic morphological features of apoptosis. Similar results were obtained using other pharmacological MEK1/2 inhibitors (e.g., PD 98059 and U0126) as well as another leukemic cell line that expresses Bcr-Abl (e.g., LAMA 84). However, synergistic induction of apoptosis by STI571 and PD184352 was not observed in human myeloid leukemia cells that do not express the Bcr-Abl kinase (e.g., HL-60 and U937) nor in normal human peripheral blood mononuclear cells. Synergistic potentiation of STI571-mediated lethality by PD184352 was associated with multiple perturbations in signaling and apoptotic regulatory pathways, including caspase-dependent down-regulation of Bcr-Abl and Bcl-2; caspase-independent down-regulation of Bcl-x(L) and Mcl-1; activation of JNK, p38 MAPK, and p34(cdc2); and diminished phosphorylation of Stat5 and CREB. Significantly, coexposure to PD184352 strikingly increased the lethality of a pharmacologically achievable concentration of STI571 (i.e., 1-2 microM) in resistant K562 cells expressing marked increases in Bcr-Abl protein levels. Together, these findings raise the possibility that treatment of Bcr-Abl-expressing cells with STI571 elicits a cytoprotective MAPK activation response and that interruption of the latter pathway (e.g., by pharmacological MEK1/2 inhibitors) is associated with a highly synergistic induction of mitochondrial damage and apoptosis. They also indicate that in the case of Bcr-Abl-positive cells, simultaneous interruption of two signal transduction pathways may represent an effective antileukemic strategy.

The constitutive photomorphogenesis 9 signalosome directs vascular endothelial growth factor production in tumor cells

Angiogenesis is a prerequisite for solid tumor growth and metastasis. Elucidation of the signaling pathways that control tumor angiogenesis constitutes the basis for a rational antiangiogenic tumor therapy. Here we show that the production of vascular endothelial growth factor (VEGF) in HeLa and HL-60 cells is directed by the constitutive photomorphogenesis 9 signalosome (CSN). The CSN is a kinase complex that cooperates with the ubiquitin/26S proteasome system in regulating the stability of proteins involved in signal transduction. VEGF expression is controlled by the transcription factors activator protein (AP)-1, AP-2, SP-1, and hypoxia-inducible factor 1. Inhibition of CSN kinase activity by 50 microM curcumin for 2 h decreases the cellular c-Jun concentration, resulting in a reduction of the VEGF production by approximately 75%. The removal of the inhibitor from the cells led to a time-dependent recovery of endogenous c-Jun that is paralleled by increasing VEGF production. Elevated cellular CSN activity induced by CSN subunit 2 overexpression causes increased VEGF production in HeLa cells. A competitor of CSN-dependent c-Jun phosphorylation, the NH(2)-terminal c-Jun fragment Deltac-Jun(1-226), inhibits VEGF production in HeLa cells. The transcription factors AP-2 and SP-1 act independently of the CSN. They contribute less than a quarter to basal VEGF production. Under our experimental conditions, hypoxia-inducible factor 1alpha protein was not detected. Overexpression of the tumor suppressor p53 reduces VEGF production in HeLa cells. p53 competes with c-Jun for CSN-specific phosphorylation with the consequence of c-Jun destabilization. We conclude that CSN-directed c-Jun signaling mediates high VEGF production in HeLa and HL-60 cells. The data provide an explanation for the known antiangiogenic and antitumorigenic activities of curcumin. Because the CSN regulates the major part of VEGF production in the tested tumor cells, it constitutes a potentially important target for tumor therapy.

Up-regulation of telomerase activity in Herpesvirus saimiri immortalized human T-lymphocytes

Human T-lymphocytes can be transformed to unlimited growth by Herpesvirus saimiri (HVS). We studied the telomerase activity of a recently established HVS immortalized human CD4 T cell clone in comparison to peripheral blood lymphocytes (PBL) and unstimulated or phytohemagglutinin (PHA)-stimulated CD4 T-cells by a Telomeric Repeat Amplification-Protocol (TRAP) -Assay. Telomerase activity in PHA-stimulated CD4 T-cells was seven-fold and in HVS-infected CD4 T-cells 14-fold higher than in untreated CD4 T-cells. The HVS immortalized T-cell clone provides a useful tool for studying the regulation of telomerase activity during carcinogenesis and for testing of telomerase-inhibitory drugs.

The activation of PI 3-K and PKC zeta in PMA-induced differentiation of HL-60 cells

The human myelocytic leukemia cell line HL-60 is a useful model for the study of cellular differentiation. Phorbol 12-myristate 13-acetate (PMA) induces the monocyte/macrophage-like differentiation of HL-60 cells and results in growth arrest, increasing adherence. In PMA-induced differentiation of HL-60 cells, phosphoinositide 3-kinase (PI 3-K) activity was measured as phosphatidylinositol3P recovery from phosphatidylinositol by in vitro kinase assay. PI 3-K activity was increased in HL-60 cells that were stimulated by 20 nM PMA and the activity was inhibited by pretreatment with 20 microM LY294002, a specific inhibitor of PI 3-K. Members of the protein kinase C (PKC) family have been suggested to be one of the downstream targets of PI 3-K. PKC zeta is one of the atypical PKCs, non-diacylglycerol-responsive PKCs, and the activity was measured by the ability of phosphorylation onto myelin basic protein. PMA also induced the activation of PKC zeta during monocytic differentiation of HL-60 cells, and LY294002-pretreated cells failed to induce PKC zeta activation. The activity of PI 3-K is essential for PKC zeta activation, and LY294002 blocks both monocytic differentiation of HL-60 cells and activation of PKC zeta during PMA-induced cell differentiation. This implies that activated PI 3-K subsequently stimulates the PKC zeta in the process of PMA-induced monocytic differentiation.

Eupatilin, a pharmacologically active flavone derived from Artemisia plants, induces apoptosis in human promyelocytic leukemia cells

Extracts of the whole herb of Artemisia asiatica Nakai (Asteraceae) have been used in traditional oriental medicine for the treatment of inflammation, cancer and other disorders. In the present work, we have evaluated the apoptosis-inducing capability of eupatilin (5,7-dihydroxy-3,4,6-trimethoxyflavone), a pharmacologically active ingredient of A. asiatica, in cultured human promyelocytic leukemia (HL-60) cells. Thus, eupatilin exhibited concentration-dependent inhibitory effects on viability and DNA synthesis capability of HL-60 cells. The anti-proliferative effect of eupatilin was attributable to its apoptosis-inducing activity as determined by characteristic nuclear condensation, in situ terminal end-labeling of fragmented DNA (TUNEL), release of mitochondrial cytochrome c into cytoplasm, proteolytic activation of caspases-9, -3, and -7, and cleavage of poly(ADP-ribose)polymerase. Eupatilin-induced HL-60 cell apoptosis does not appear to be mediated via alteration in Bcl-2/Bax-2. Taken together, the above findings suggest that eupatilin has chemopreventive and cytotoxic effects.

Differential involvement of caspases in hydroquinone-induced apoptosis in human leukemic hl-60 and jurkat cells

The benzene metabolite hydroquinone (HQ) is postulated to exert its myelotoxicity by bioactivation to reactive quinone derivatives in myeloperoxidase (MPO)-containing cells. In this study, the role of caspases in hydroquinone-induced apoptosis in MPO-rich HL-60 promyelocytic leukemia and MPO-deficient Jurkat T-lymphoblastic leukemia cells was investigated. HQ-induced apoptosis in both cell types was accompanied by phosphatidylserine (PS) exposure, caspases-3/-7 activation, PARP cleavage, DNA fragmentation, and ultrastructural changes as assessed by electron microscopy. In HL-60 cells, the general caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp fluoromethyl ketone (Z-VAD.FMK) blocked activation of caspases-3/-7, cleavage of PARP, and DNA, but PS externalization and cytoplasmic changes were not significantly affected. In marked contrast, all features of apoptosis were completely inhibited by Z-VAD.FMK in HQ-treated Jurkat cells. These data provide evidence for Z-VAD.FMK-insensitive and caspases-3/-7-independent pathway(s) in the externalization of PS and cytoplasmic changes during HQ-induced apoptosis in HL-60 cells. In contrast, in Jurkat cells, all of these changes required caspase activation. The ability of HQ to induce equivalent apoptosis in both MPO-deficient Jurkat cells and MPO-rich HL-60 cells demonstrates that MPO-catalyzed bioactivation of HQ is not a prerequisite for toxicity. The differential mechanisms of apoptosis in HL-60 and Jurkat T cells may reflect the MPO activity of these cells and, as a result, the amount of reactive BQ and other metabolites that are generated.

Se-methylselenocysteine induces apoptosis mediated by reactive oxygen species in HL-60 cells

Recent studies have implicated apoptosis as one of the most plausible mechanisms of the chemopreventive effects of selenium compounds, and reactive oxygen species (ROS) as important mediators in apoptosis induced by various stimuli. In the present study, we demonstrate that Se-methylselenocysteine (MSC), one of the most effective selenium compounds at chemoprevention, induced apoptosis in HL-60 cells and that ROS plays a crucial role in MSC-induced apoptosis. The uptake of MSC by HL-60 cells occurred quite early, reaching the maximum within 1 h. The dose-dependent decrease in cell viability was observed by MSC treatment and was coincident with increased DNA fragmentation and sub-G(1) population. 50 microM of MSC was able to induce apoptosis in 48% of cell population at a 24 h time point. Moreover, the release of cytochrome c from mitochondria and the activation of caspase-3 and caspase-9 were also observed. The measurement of ROS by dichlorofluorescein fluorescence revealed that dose- and time-dependent increase in ROS was induced by MSC. N-acetylcysteine, glutathione, and deferoxamine blocked cell death, DNA fragmentation, and ROS generation induced by MSC. Moreover, N-acetylcysteine effectively blocked caspase-3 activation and the increase of the sub-G(1) population induced by MSC. These results imply that ROS is a critical mediator of the MSC-induced apoptosis in HL-60 cells.

Regulation of the catalase gene promoter by Sp1, CCAAT-recognizing factors, and a WT1/Egr-related factor in hydrogen peroxide-resistant HP100 cells

Reactive oxygen species play a critical role in the onset of apoptosis induced by various extracellular stimuli, including ionizing radiation. Therefore active regulation of reactive oxygen species-metabolizing enzymes may be one response to an apoptotic stimulus. In this regard, HP100 cells, H(2)O(2)-resistant variants derived from human leukemia HL60 cells, display an interesting phenotype in which the activity of catalase is constitutively high, whereas its mRNA is reduced after X-ray irradiation. In the present study, we investigated the molecular mechanisms underlying this phenomenon. By combining analyses from nuclear run-on, reporter gene transient transfection, genomic footprinting, site-directed mutagenesis, electrophoretic mobility shift analysis, and Western blotting experiments, we found that constitutively elevated catalase expression is strongly regulated at the transcriptional level by both Sp1 and CCAAT-recognizing factors and that much higher levels of nuclear Sp1 and NF-Y are present in HP100 nuclei as compared with HL60 nuclei. In addition, we demonstrated an X-ray-inducible association of a WT1/Egr-related factor with an overlapping Sp1/Egr-1 recognition sequence located within the core promoter of the catalase gene. This association may lead to inactivation of the promoter by disturbing or competing with the transactivating ability of Sp1.

Pharmacological inhibitors of the mitogen-activated protein kinase (MAPK) kinase/MAPK cascade interact synergistically with UCN-01 to induce mitochondrial dysfunction and apoptosis in human leukemia cells

Interactions between the checkpoint abrogator UCN-01 and several pharmacological inhibitors of the mitogen-activated protein kinase (MAPK) kinase (MEK)/MAPK pathway have been examined in a variety of human leukemia cell lines. Exposure of U937 monocytic leukemia cells to a marginally toxic concentration of UCN-01 (e.g., 150 nM) for 18 h resulted in phosphorylation/activation of p42/44 MAPK. Coadministration of the MEK inhibitor PD184352 (10 microM) blocked UCN-01-induced MAPK activation and was accompanied by marked mitochondrial damage (e.g., cytochrome c release and loss of DeltaPsi(m)), caspase activation, DNA fragmentation, and apoptosis. Similar interactions were noted in the case of other MEK inhibitors (e.g., PD98059; U0126) as well as in multiple other leukemia cell types (e.g., HL-60, Jurkat, CCRF-CEM, and Raji). Coadministration of PD184352 and UCN-01 resulted in reduced binding of the cdc25C phosphatase to 14-3-3 proteins, enhanced dephosphorylation/activation of p34(cdc2), and diminished phosphorylation of cyclic AMP-responsive element binding protein. The ability of UCN-01, when combined with PD184352, to antagonize cdc25C/14-3-3 protein binding, promote dephosphorylation of p34(cdc2), and potentiate apoptosis was mimicked by the ataxia telangectasia mutation inhibitor caffeine. In contrast, cotreatment of cells with UCN-01 and PD184352 did not substantially increase c-Jun-NH(2)-terminal kinase activation nor did it alter expression of Bcl-2, Bcl-x(L), Bax, or X-inhibitor of apoptosis. However, coexposure of U937 cells to UCN-01 and PD184352 induced a marked increase in p38 MAPK activation. Moreover, SB203580, which inhibits multiple kinases including p38 MAPK, partially antagonized cell death. Lastly, although UCN-01 +/- PD184352 did not induce p21(CIP1), stable expression of a p21(CIP1) antisense construct significantly increased susceptibility to this drug combination. Together, these findings indicate that exposure of leukemic cells to UCN-01 leads to activation of the MAPK cascade and that interruption of this process by MEK inhibition triggers perturbations in several signaling and cell cycle regulatory pathways that culminate in mitochondrial injury, caspase activation, and apoptosis. They also raise the possibility that disrupting multiple signaling pathways, e.g., by combining UCN-01 with MEK inhibitors, may represent a novel antileukemic strategy.

Immunocytochemical localization of peptidylarginine deiminase in human eosinophils and neutrophils

Peptidylarginine deiminase, registered as PAD V in the DDBJ/GenBank/EMBL data banks, is expressed in HL-60 cells differentiated into granulocytes or monocytes. We analyzed PAD activities in density-fractionated human peripheral blood cell fractions. PAD activity with similar substrate specificity to that of PAD V was found in the eosinophil and neutrophil fractions, which showed single bands comigrating with authentic PAD V on immunoblotting with an anti-PAD V antibody. Both the biochemical and immunoblotting analyses showed marked enrichment of PAD V in the eosinophil fraction. Its immunoreactivity appeared to localize in eosinophilic granules at high density and in myeloperoxidase-negative cytoplasmic granules of neutrophils at low density, as determined by confocal laser-scanning microscopy. Possible roles of PAD V in myeloid differentiation and granulocyte function are discussed. In addition, we present evidence for the presence of PAD(s) that are antigenically different from PAD V in monocytes and lymphocytes.

Involvement of cytosolic prolyl endopeptidase in degradation of p40-phox splice variant protein in myeloid cells

Our previous studies indicated that an alternatively spliced variant mRNA of p40-phox, a cytosolic component of NADPH oxidase, is expressed but its protein is hardly detected in myeloid cells such as promyelocytic HL-60 cells and neutrophils. Here, we have examined the stability of p40-phox variant protein in undifferentiated HL-60 cells. When in vitro-translated proteins were incubated with subcellular fractions of HL-60 cells, p40-phox variant protein but not native p40-phox was degraded by the cytosol and granule fractions. The degradation of variant protein by the granule fraction was observed using sonicated but not intact granules, suggesting that the variant protein is unlikely to be degraded by the granules in intact cells. To identify the enzyme(s) involved, we examined the effects of various enzyme inhibitors on the degradation of variant protein by the cytosol fraction. Degradation was completely inhibited by proline-specific serine protease (prolyl endopeptidase) inhibitors but not by proteasome, calpain, and metalloprotease inhibitors. Furthermore, the variant protein was degraded by a purified prolyl endopeptidase, and the degradation was protected by treating HL-60 cells with a cell-permeable inhibitor (S17092-1) for prolyl endopeptidase. These observations suggest that a cytosolic prolyl endopeptidase is involved in the degradation of p40-phox variant protein in myeloid cells.

Homocysteine thiolactone induces apoptotic DNA damage mediated by increased intracellular hydrogen peroxide and caspase 3 activation in HL-60 cells

The cytotoxicity of homocysteine derivatives on chromosomal damage in somatic cells is not well established. The present study used reactive homocysteine derivative of homocysteine thiolactone (Hcy) to investigate its causal effect on apoptotic DNA injury in human promyeloid HL-60 cells. Our results demonstrated that Hcy induced cell death and features of apoptosis including increased phosphotidylserine exposure on the membrane surface, increased apoptotic cells with hypoploid DNA contents, and internucleosomal DNA fragmentation, all of which occurred in a time- and concentration-dependent manner. Hcy treatment also significantly increased intracellular reactive oxygen species H2O2, which coincided with the elimination of caspase 3 proenzyme levels and increased caspase 3 activity at the time of the appearance of apoptotic DNA fragmentation. Preincubation of Hcy-treated HL-60 cells with catalase completely scavenged intracellular H2O2, thus inhibiting caspase 3 activity and protecting cells from apoptotic DNA damage. In contrast, superoxide dismutase failed to inhibit Hcy-induced DNA damage. Taken together, these results demonstrate that Hcy exerted its genotoxic effects on HL-60 cells through an apoptotic pathway, which is mediated by the activation of caspase 3 activity induced by an increase in intracellular hydrogen peroxide.