Cyclosporin a Potentiates the Cytotoxic Effects of Methyl Methanesulphonate in HL-60 and K562 Cells

Methyl methanesulphonate (MMS) is a DNA damaging agent, which induces oxidative stress, ATP depletion, and consequently, cell death, in HL-60 and K562 cells. The cell death induced by MMS predominantly exhibited the morphological and biochemical hallmarks of necrosis. A minor population of dying cells exhibited apoptotic hallmarks, especially in K562 cell cultures. Cyclosporin A (CsA) was used to modulate the MMS-induced cell death. Our results indicated that CsA did not prevent cells from dying, but changed the mode of death from necrotic to apoptotic. Surprisingly, CsA enhanced oxidative stress and increased the overall number of dead cells. Based on these results, we conclude that the modulatory effect of CsA on MMS-induced cell death might arise from an interference by CsA with mitochondrial metabolism, rather than from inhibition of the MMS efflux mediated by P-glycoprotein.

Increased 14-3-3ζ expression in the multidrug-resistant leukemia cell line HL-60/VCR as compared to the parental line mediates cell growth and apoptosis in part through modification of gene expression

BACKGROUND

Acute myeloid leukemia (AML) recurrence is largely a result of multidrug resistance (MDR). We aimed to examine the role of 14-3-3ζ in AML chemosensitivity using HL-60 and vincristine-resistant HL-60/VCR cells.

METHODS

The effects of 14-3-3ζ siRNA on the growth and cell cycle progression of HL-60 and HL-60/VCR cells were determined. The effect of 14-3-3ζ siRNA on topotecan (TPT)-induced apoptosis was evaluated by several assays.

RESULTS

Compared to HL-60 cells, HL-60/VCR cells had increased 14-3-3ζ mRNA and protein expression. Increased mdr-1 mRNA as well as mdr-1, Bcl-2 and Mcl-1 protein expression were observed in HL-60/VCR cells. In both HL-60 and HL-60/VCR cells, 14-3-3ζ was observed in the cytoplasm and nuclear compartments. 14-3-3ζ siRNA significantly reduced HL-60 and HL-60/VCR cell growth after 48 h and increased the proportion of cells in the G0/G1 phase. Moreover, 14-3-3ζ siRNA significantly increased the sensitivity of both HL-60 and HL-60/VCR cells to TPT, possibly through the inhibition of Bcl-2, Mcl-1 and mdr-1 protein expression.

CONCLUSIONS

Silencing of 14-3-3ζ increased the sensitivity of both sensitive and resistant HL-60 cells to TPT-induced apoptosis, possibly through altering the expression of apoptosis-associated proteins, suggesting that it may be a potential target for MDR AML.

Induction of non-apoptotic cell death in human oral squamous cell carcinoma cell lines by Rhinacanthus nasutus extract

BACKGROUND

We recently reported that the MeOH extract of aerial parts and root of Rhinacanthus nasutus showed diverse biological activity, with most activity being concentrated into the EtOAc layer separated by sequential organic solvent extractions. In the present study, the EtOAc extracts were further separated by silica-gel column chromatography into five fractions (Frs. 1-5), and their cytotoxicity and apoptosis-inducing activity investigated.

MATERIALS AND METHODS

Cytotoxic activity was determined by 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) method. The 50% cytotoxic concentration (CC(50)) was determined from the dose-response curve. Tumor specificity (TS) was determined by the ratio of the mean CC(50) for normal cells to the one for tumor cell lines. DNA fragmentation was assayed by agarose gel electrophoresis. Caspase-3/-7 activation was monitored by cleavage of substrates either spectrophotometrically or by western blot analysis.

RESULTS

Among five fractions of the EtOAc extract, Fr. 1, eluted with CHCl(3)-MeOH (50:1), showed the highest tumor specificity (TS=3.3) as compared with other fractions eluted at higher concentrations of MeOH in CHCl(3) (TS=1.0-2.8). Fr. 1 did not induce internucleosomal DNA fragmentation or induced only marginal level of caspase-3 activity in either human promyelocytic leukemia HL-60 cells and human oral squamous cell carcinoma (OSCC) cell lines HSC-2.

CONCLUSION

The present study suggests that hydrophobic substances of EtOAc extract show tumor specific cytotoxicity by inducing little or no apoptosis.

Induction of non-apoptotic cell death by Odontioda Marie Noel 'Velano' extracts in human oral squamous cell carcinoma cell lines

BACKGROUND

We recently reported that the MeOH extract from bulbs of Odontioda Marie Noel 'Velano' exhibited diverse biological activities but most of the activity was concentrated into the EtOAc layer separated by sequential organic solvent extractions. In the present study, the EtOAc layer was subjected to silica-gel column chromatography for further separation into five fractions, and the cytotoxicity and apoptosis-inducing activity of the fractions against human normal oral and tumor cells was further investigated.

MATERIALS AND METHODS

Cytotoxic activity was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. The 50% cytotoxic concentration (CC(50)) was determined by the dose-response curve. Tumor specificity (TS) was determined by the ratio of the mean CC(50) for normal cells to the one of tumor cell lines. DNA fragmentation was assayed by agarose gel electrophoresis, caspase-3/-7 activation was monitored by cleavage of substrates either spectrophotometrically or by western blot analysis.

RESULTS

Among five fractions, the most hydrophobic fraction (Fr. 1) showed the highest cytotoxicity against all cell lines tested, followed by Fr. 2 >Fr. 3 >Fr. 4 >Fr. 5, in order of increasing polarity. Fr. 2 had the highest tumor-specificity, followed by Fr. 3, Fr. 4, Fr. 1 and Fr. 5. Fr. 1 induced caspase-3 activation more potently in promyelocytic leukemia HL-60 cells, than in oral squamous cell carcinoma (OSCC) HSC-2 cells, whereas it did not induce internucleosomal DNA fragmentation in either of these cell lines.

CONCLUSION

The present study suggests that hydrophobic substances in the EtOAc extract of Odontioda Marie Noel 'Velano' exhibit tumor-specific cytotoxicity without inducing apoptosis in the HSC-2 OSCC cell line.

Regulation of desaturase expression in HL60 cells

The expression of delta 5 desaturase (D5D), delta 6 desaturase (D6D) and delta 9 desaturase (D9D) was determined by RT-PCR in the human promyelocytic cell line HL60. During 72 h of culture with 10% FBS, D5D and D6D were upregulated 5 to 6-fold, whereas D9D approximately doubled. The addition of fatty acids (FAs) to the culture medium suppressed upregulation of all desaturases. N-3 and n-6 FA appeared to be more effective than n-9 or saturated FA. When FAs were added after 72 h, further upregulation during the next 24 h was suppressed for nearly all desaturases and FAs tested, except for D5D when oleic acid (OA) or stearic acid (SA) was added. In cells cultured with restricted amounts of FBS, desaturase expression increased with decreasing concentrations of FBS. Cellular FA content decreased by 60% in the neutral lipid fraction, whereas that of the phospholipid fraction decreased by 10% during 72 h of culture. The largest decrease occurred in the sum of n-3 and n-6 FA of the neutral lipid fraction, which was reduced by 83%, whereas the content of these FAs in the phospholipid fraction decreased by 32%. The results indicate that when the supply of FA to HL60 cells is limited, the intracellular content of n-3 and n-6 FA decreases and this leads to upregulation of the desaturases, particularly D5D and D6D. Since HL60 cells resemble human leukocytes, the results suggest that desaturase expression in leukocytes may be exploited as a biomarker for FA status.

Epigenetic and genetic mechanisms contribute to telomerase inhibition by EGCG

The ends of human chromosomes are protected from the degradation associated with cell division by 15-20 kb long segments of hexameric repeats of 5'-TTAGGG-3' termed telomeres. In normal cells telomeres lose up to 300 bp of DNA per cell division that ultimately leads to senescence; however, most cancer cells bypass this lifespan restriction through the expression of telomerase. hTERT, the catalytic subunit essential for the proper function of telomerase, has been shown to be expressed in approximately 90% of all cancers. In this study we investigated the hTERT inhibiting effects of (-)-epigallocatechin-3-gallate (EGCG), the major polyphenol found in green tea catechins, in MCF-7 breast cancers cells and HL60 promyelocytic leukemia cells. Exposure to EGCG reduced cellular proliferation and induced apoptosis in both MCF-7 and HL60 cells in vitro, although hTERT mRNA expression was decreased only in MCF-7 cells when treated with EGCG. Furthermore, down-regulation of hTERT gene expression in MCF-7 cells appeared to be largely due to epigenetic alterations. Treatment of MCF-7 cells with EGCG resulted in a time-dependent decrease in hTERT promoter methylation and ablated histone H3 Lys9 acetylation. In conjunction with demethylation, further analysis showed an increase in hTERT repressor E2F-1 binding at the promoter. From these findings, we propose that EGCG is effective in causing cell death in both MCF-7 and HL60 cancer cell lines and may work through different pathways involving both anti-oxidant effects and epigenetic modulation.

NAD(P)H:quinone oxidoreductase (NQO1) loss of function in Burkitt's lymphoma cell lines

Two-electron reduction of quinones catalyzed by NAD(P)H:quinone oxidoreductase (NQO1) protects cells against oxidative stress and toxic quinones. In fact, low level of NQO1 activity is often associated with increased risk of developing different types of tumours and with toxic effects linked to environmental quinones. In a previous report we analyzed the relationship between the oxidative stress induced by UV radiation and CoQ10 content in Burkitt's lymphoma cell lines compared to HL-60. The basal content of CoQ10 in Raji cells was slightly higher compared to HL-60. Moreover, after irradiation or ubiquinone supplementation in the medium, reduced CoQ10 levels were higher in Raji and Daudi cells compared to HL-60. In the present work, in order to inquire if NQO1 plays a role in the CoQ reducing capacity observed in the lymphoblastoid cell lines, we analyzed the transcription and translation products of this gene in Raji and Daudi cells, compared to cell lines possessing low and high NQO1 activity. The amount of transcripts of this gene in lymphoblastoid cells was comparable to that observed in HL-60 cells (low activity), as well as the level of two alternatively spliced mRNAs; one of which is described for the first time in this work. From the genotype analysis of polymorphisms C609T and C465T we observed that HL-60, Raji and Daudi cells were all heterozygous. Furthermore, NQO1 enzyme activity and protein synthesis in the cytosol of Raji and Daudi cells were undetectable. Therefore in Burkitt's lymphoma cell lines the NQO1 gene is not efficiently translated and this effect is not related to (C609T) polymorphism. Further studies will be necessary to find the enzyme responsible for CoQ10 reducing activity observed in lymphoma cell lines. On the other hand, this result suggests a careful re-evaluation of data concerning loss of NQO1 activity and polymorphisms in tumour cells.

Caspase-8 preferentially senses the apoptosis-inducing action of NG-18, a Gambogic acid derivative, in human leukemia HL-60 cells

Gambogic acid (GA) is the major active ingredient of gamboge secreted from a Chinese traditional medicine Garcinia hanburryi possessing potent anti-tumor activity. N-(2-ethoxyethyl)gambogamide (NG-18), a derivative of GA, also efficiently inhibits proliferation of cultured human tumor cells. The inhibition effect of NG-18 is associated with its ability to induce apoptosis. In the present study, NG-18 markedly induced leukemia HL-60 cells apoptosis, and the extrinsic and intrinsic apoptosis pathways were activated almost at the same time. NG-18-induced tumor cell apoptosis was associated with up-regulation of pro-apoptotic Bcl-2 family member Bax, and downregulation of anti-apoptotic protein Bcl-2. The NG-18-induced apoptosis was blocked completely by a pan-caspase inhibitor Z-VAD-FMK, indicating that caspases were functionally and actively involved in this process. The specific inhibition of caspase-8 activity using Z-IETD-FMK significantly blocked NG-18-induced apoptosis. In contrast, inhibition of other initiator caspases, caspase-2 or -9, using Z-VDVAD-FMK or Z-LEHD-FMK respectively had no effect on NG-18-induced apoptosis. Altogether, our data demonstrated that NG-18-induced apoptosis was dependent on caspases and caspase-8 acted as a key executor in the event.

Epicatechin conjugated with fatty acid is a potent inhibitor of DNA polymerase and angiogenesis

Anti-cancer and anti-angiogenesis effects of green tea catechins have been demonstrated. It has been found that chemical modification of tea catechins improves their biological activities. We examined the chemical modification of epicatechin enhanced anti-cancer and anti-angiogenic effects. Epicatechin conjugated with fatty acid (acyl-catechin) strongly inhibited DNA polymerase activity, HL-60 cancer cell growth and angiogenesis. Epicatechin conjugated with palmitic acid ((2R,3R)-3',4',5,7-tetrahydroxyflavan-3-yl hexadecanoate, epicatechin-C16) was the strongest inhibitor in DNA polymerase alpha, beta, lambda and angiogenesis assays. Epicatechin-C16 also suppressed human endothelial cell (HUVEC) tube formation on reconstituted basement membrane, suggesting that it affected not only DNA polymerase activity but also the signal transduction pathways needed for the tube formation in HUVECs. These results suggest that acylation of epicatechin is an effective chemical modification to improve the anti-cancer activity of epicatechin.

The role of p38 MAPK activation in auranofin-induced apoptosis of human promyelocytic leukaemia HL-60 cells

In a previous study, we reported an antileukaemic activity of auranofin (AF), demonstrating its dual effects: on the induction of apoptotic cell death and its synergistic action with retinoic acid on cell differentiation. In this study, we investigated the downstream signalling events of AF-induced apoptosis to determine the molecular mechanisms of AF activity. Treatment of HL-60 cells with AF induced apoptosis in a concentration- and time-dependent manner. Western blot analysis showed that AF-induced apoptosis was accompanied by the activation of caspase-8, caspase-9, and caspase-3, and the release of cytochrome c from the mitochondria. The phosphorylation and kinase activities of p38 mitogen-activated protein kinase (p38 MAPK) increased gradually until 12 h after AF (2 microM) treatment, and p38 MAPK was also activated concentration-dependently. Pretreatment with SB203580, a specific inhibitor of p38 MAPK, significantly blocked DNA fragmentation and the cleavage of procaspase-8, procaspase-3, and poly-ADP-ribose polymerase (PARP), whereas SB203580 alone had no effect. Reactive oxygen species (ROS) were also detected within 1 h after AF treatment, and the antioxidant N-acetyl-L-cysteine (NAC) effectively protected the cells from apoptosis by inhibiting the phosphorylation of p38 MAPK and the activation of caspases. These results suggest that ROS generation and the subsequent activation of p38 MAPK are essential for the proapoptotic effects of AF in human promyelocytic leukaemia HL-60 cells.

Characterization of a serine protease-mediated cell death program activated in human leukemia cells

Tightly controlled proteolysis is a defining feature of apoptosis and caspases are critical in this regard. Significant roles for non-caspase proteases in cell death have been highlighted. Staurosporine causes a rapid induction of apoptosis in virtually all mammalian cell types. Numerous studies demonstrate that staurosporine can activate cell death under caspase-inhibiting circumstances. The aim of this study was to investigate the proteolytic mechanisms responsible for cell death under these conditions. To that end, we show that inhibitors of serine proteases can delay cell death in one such system. Furthermore, through profiling of proteolytic activation, we demonstrate, for the first time, that staurosporine activates a chymotrypsin-like serine protease-dependent cell death in HL-60 cells independently, but in parallel with the caspase controlled systems. Features of the serine protease-mediated system include cell shrinkage and apoptotic morphology, regulation of caspase-3, altered nuclear morphology, generation of an endonuclease and DNA degradation. We also demonstrate a staurosporine-induced activation of a putative 16 kDa chymotrypsin-like protein during apoptosis.

Intrinsic pathway of hydroquinone induced apoptosis occurs via both caspase-dependent and caspase-independent mechanisms

The role of mitochondria and apical caspases in apoptosis induced by the benzene metabolite hydroquinone (HQ) remains to be elucidated. Here, we investigated the involvement of mitochondria and activation of the apical caspases-8 and -9 in HQ induced apoptosis in myeloperoxidase (MPO)-rich HL-60 and MPO-deficient Jurkat T cells. Treatment of HL-60 and Jurkat cells with HQ resulted in apoptosis as assessed by phosphatidyl serine (PS) exposure, loss of mitochondrial transmembrane potential (MTP), release of cytochrome c, and processing of apical caspases-8 and -9 and executioner caspase-3. In HQ-treated HL-60 cells, pretreatment with the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethyl ketone (ZVAD), which did not inhibit PS exposure, also failed to abrogate the loss of MTP and release of cytochrome c. However, complete processing of caspase-9 was inhibited in the presence of ZVAD. In marked contrast, in HQ-treated Jurkat cells, ZVAD significantly abrogated PS exposure, loss of MTP, and caspase-9 processing but not release of cytochrome c. Although ZVAD-sensitive caspase-8 processing occurred in both cell types, pretreatment with either fas-receptor blocking ZB4 or fas-ligand NOK1 neutralizing antibodies did not inhibit HQ-induced apoptosis. In conclusion, our results demonstrate that HQ induced apoptosis in Jurkat cells occurs via a ZVAD-inhibitable, caspase-dependent process, while in HL-60 cells, apoptosis occurs predominantly via caspase-independent mechanisms. Our results emphasize that both caspase-dependent and independent mechanisms should be considered in the intrinsic apoptotic pathway induced by HQ.

Potent inhibition of human telomerase by helenalin

Telomerase activity is repressed in normal human somatic cells, but is activated in most cancers, suggesting that telomerase may be an important target for cancer therapy. Inhibition of telomerase in cancer cells has been shown to limit the growth of human cancer cells in culture. In this study, we report that helenalin, a natural sesquiterpene lactone, is a potent and selective inhibitor for human telomerase. In vitro studies indicate that this drug can inactivate telomerase directly in a manner that is dependent on concentration and time. The inhibitory action of this drug on telomerase is selective since the presence of excessive externally added proteins did not protect the inhibition and all of the other enzymes tested in this study were not inhibited by this drug. Furthermore, we demonstrated that helenalin can inhibit the expression of hTERT and telomerase in hematopoietic cancer cells. Therefore, the anti-tumor activity of helenalin is attributed, at least in part, to the inhibition of telomerase.

Regulation of aminopeptidase N (EC 3.4.11.2; APN; CD13) by interferon-gamma on the HL-60 cell line

Membrane-bound peptidases play important roles in the regulation of local concentrations of various signalling peptides such as the growth factors, hormones, chemokines and cytokines. That is accomplished by means of their enzyme activity. Recently, membrane-bound peptidases have also been shown to act as receptors, receiving signals from as yet undefined ligands and transducing them into the cell interior. By using either or both of these mechanisms, peptidases interact with fundamental cellular functions: growth, differentiation, activation and death. This study addressed the effects of a T-cell derived cytokine, interferon-gamma (IFN-gamma) on the activity of aminopeptidase N (APN), an ectoenzyme processing several signal peptides. Cells of a myelo-monocytic cell line HL-60 were used as a model system, and APN was assayed at the levels of mRNA, its membrane marker CD13, and the enzyme activity. Regulation of CD13/APN by IFN-gamma was found at all three levels. The direction of regulation was time-dependent: an initial down-regulation seen 24 and 48 hrs after the onset of treatment with IFN-gamma was replaced by an up-regulation after 72 and/or 96 hrs. Up-regulation of CD13/APN observed after 96 hrs was preceded by an up-regulation of APN mRNA reaching its maximum after 72 hrs. The IFN-gamma-induced regulation of APN was due to membrane aminopeptidase N, since it could be completely abrogated by an APN blocking antibody WM-15. The delayed up-regulation of CD13/APN (observed after 72 and/or 96 hrs), required de novo protein synthesis as it could be abrogated by cycloheximide, an inhibitor of protein synthesis. Possible role of endogenous (IFN-gamma-induced) TGF-beta in mediating CD13/APN up-regulation could be excluded, since no TGF-beta was found in supernatants of IFN-gamma treated HL-60 cells. Thus, our data show regulation of CD13/APN on cells of myelo-monocytic origin by a T-cell derived cytokine, IFN-gamma. A similar mechanism might play a role in inflammation.

Effects of 2,2',4,4'-Tetrachlorobiphenyl on Granulocytic HL-60 Cell Function and Expression of Cyclooxygenase-2

Polychlorinated biphenyls (PCBs) are persistent environmental contaminants that affect a number of cellular systems, including neutrophils. It has been demonstrated that noncoplanar PCBs (i.e., ortho- substituted PCBs) alter function of primary rat neutrophils. The objectives of these experiments were to determine if responses in a human, neutrophil-like cell line exposed to PCBs were similar to those reported for rat neutrophils and to explore further PCB-mediated alterations in neutrophil function. The human promyelocytic leukemia cell line (HL-60) was differentiated with DMSO to a neutrophil-like phenotype. Treatment of differentiated HL-60 cells with 2,2',4,4'-tetrachlorobiphenyl, a noncoplanar, ortho-substituted PCB congener, caused an increase in f-Met-Leu-Phe-induced degranulation, as measured by release of myeloperoxidase (MPO). Treatment with the coplanar, non-ortho-substituted congener 3,3',4,4'-tetrachlorobiphenyl had no effect on MPO release. 2,2',4,4'-Tetrachlorobiphenyl caused a time- and dose-dependent release of [3H]-arachidonic acid (3H-AA). A significant increase in 3H-AA release was observed after 60 min of exposure, and concentrations of 10 microM or larger increased 3H-AA release. In contrast, 3,3',4,4'-tetrachlorobiphenyl had no effect on 3H-AA release. The effect of PCBs on mRNA levels for cyclooxygenase-2 (COX-2) was examined using semiquantitative RT-PCR. COX-2 mRNA was significantly elevated in response to 2,2',4,4'-tetrachlorobiphenyl in a concentration-dependent manner. COX-2 expression was maximal by 30 min of exposure to 2,2',4,4'-tetrachlorobiphenyl. COX-2 protein and activity were also increased after exposure to 2,2',4,4'-tetrachlorobiphenyl; COX-1 protein and activity were unaffected. 3,3',4,4'-Tetrachlorobiphenyl did not increase COX-2 mRNA levels. These results demonstrate that a noncoplanar PCB alters the functional status of granulocytic HL-60 cells, causing enhanced degranulation and upregulation of COX-2, whereas a coplanar PCB lacks this activity. These data suggest that noncoplanar PCBs alter HL-60 cell function and COX-2 expression via an Ah-receptor-independent mechanism.

Proteasome proteolytic activity in hematopoietic cells from patients with chronic myeloid leukemia and multiple myeloma

BACKGROUND AND OBJECTIVES

The proteasome is a multicatalytic complex found in all eukaryotic cells; it is responsible for the degradation of key regulatory proteins associated with the cell cycle and apoptosis. In vitro, proteasome inhibitors can induce selective apoptosis in some malignant cell types as opposed to in their normal counterparts and first generation compounds are currently in clinical trials for the treatment of multiple myeloma. The objective of our study was to develop a method to extract and measure functional proteasome activity in primary human cells so that this method could then be used to determine whether patients might benefit from proteasome inhibitor therapy.

DESIGN AND METHODS

Optimal proteasome extraction and assay conditions were established with myeloma and leukemic cell lines. These conditions were then applied to primary human cells from patients. Proteasome was extracted using lysis buffer and activity measured as turnover of a peptide fluorescent substrate.

RESULTS

Cells expressing bcr-abl showed significantly higher proteasome levels (372+/-16 AFU/1x10(6) cells/min) than did bcr-abl-negative cells (151+/- 8 AFU/1x10(6) cells/min) and were more sensitive to induction of apoptosis by proteasome inhibitor. Human myeloid leukemia cell lines showed higher levels of activity than those representing myeloma (eg HL-60 cells 947+/-25 AFU/1x10(6) cells/min; U266 177+/-6 AFU/1x10(6) cells/min). Primary cells from patients had similar levels of activity to those of the comparable cell line model.

INTERPRETATION AND CONCLUSIONS

This simple method measures functional proteasome activity in primary leukemic cells and demonstrates for the first time that this activity is higher in myeloid leukemia than in myeloma cells.

Protein expression of PDZ-binding kinase is up-regulated in hematologic malignancies and strongly down-regulated during terminal differentiation of HL-60 leukemic cells

PBK/TOPK is a recently identified 322 amino acid serine/threonine kinase that is phosphorylated during mitosis and may include p38 MAPK among its targets. Previous work has shown up-regulated expression of PBK/TOPK mRNA in a variety of tumor cell lines and fetal tissues, suggesting a role for this kinase in malignant cell proliferation. In this paper, PBK/TOPK protein expression was examined in a variety of primary hematologic neoplasms: PBK/TOPK was readily detected in 9 of 12 AML samples (75%), in 3 of 3 ALL samples, and in 1 sample each of a plasmacytoma and blastic type mantle cell lymphoma where it was strongly expressed. In contrast, PBK/TOPK was only weakly expressed in 2 samples of G-CSF-mobilized peripheral blood stem cells that were enriched in CD34+ progenitors by immunoselection. Furthermore, when HL-60 myeloid leukemic cells were differentiated with phorbol ester (TPA), PBK/TOPK protein expression was strongly down-regulated by 24 h. Under these same conditions, phosphorylated c-Myc was rapidly down-regulated (by 4 h), while the levels of cyclin D1 and phosphorylated p38 were constant. Notably, of 5 clinical samples that strongly expressed PBK/TOPK, 4 also strongly expressed phosphorylated c-Myc, while only 1 of 3 PBK/TOPK negative samples expressed phosphorylated c-Myc. These data show that PBK/TOPK protein is up-regulated in a variety of hematologic malignancies and may be involved in leukemic cell growth. Additional studies are warranted to determine if PBK/TOPK would be a valuable target for novel therapeutics. To this end, we also describe the derivation of clones of 293 (human embryonic kidney) cells, which carry an inducible kinase-defective mutant of PBK/TOPK. This model may be useful for studying the effects of down-regulated PBK/TOPK function.

Induction of antioxidant enzymes by FAK in a human leukemic cell line, HL-60

We have established several focal adhesion kinase (FAK) cDNA-transfected HL-60 (HL-60/FAK) cells which were highly resistant to oxidative stress-induced apoptosis. To identify target genes that are involved in HL-60/FAK cells, we performed cDNA microarray screening using apoptosis-chip. There, we identified the decrease of glutathione peroxidase (GPx). This result prompted us to investigate the changes of antioxidant enzymes. Here, we demonstrate that lipid peroxidation was suppressed after treatment with hydrogen peroxide in HL-60/FAK cells but not vector-transfected HL-60 (HL-60/Vect) cells. Furthermore, we demonstrate that HL-60/FAK cells have higher basal reactive oxygen species (ROS) levels than the parental HL-60 or HL-60/Vect cells, while ROS accumulation by hydrogen peroxide treatment was almost the same in these cells. Basal activity and mRNA expression of antioxidant enzymes, particularly of GSH reductase (GRe), phospholipid hydroperoxide glutathione peroxidase (PHGPx) were markedly elevated in HL-60/FAK cells. In contrast, GPx and catalase levels were decreased in HL-60/FAK cells. Further, a Src family kinases inhibitor, PP2, suppressed GRe and PHGPx mRNA by inactivation of FAK and c-Src in HL-60/FAK cells. These results suggest that FAK upregulates antioxidant enzymes and suppresses lipid peroxidation, resulting in the anti-apoptotic state for oxidative stress.

Expression and induction of CYP4F subfamily in human leukocytes and HL60 cells

We investigated the expression of the CYP4F subfamily in human leukocytes and HL60 cells. Enzymatic activity assay, immunocytochemical staining, and reverse transcription-polymerase chain reaction (RT-PCR) analysis of human leukocytes showed that polymorphonuclear leukocytes (PMNs) expressed CYP4F3B and CYP4F12 in addition to CYP4F3. Transcription start site of CYP4F3B mRNA in the leukocytes was identical to that of CYP4F3 mRNA. The HL60 cells, which were differentiated into PMN-like shapes by treatment with all-trans-retinoic acid (RA), also expressed CYP4F3, CYP4F3B and CYP4F12. CYP4F3 was expressed in one third of the peripheral monocytes, which omega-hydroxylated leukotriene B(4) (LTB(4)) at a rate 11 times lower than that of PMN. The cells that were differentiated into a form similar to monocytes/macrophages in shape by treatment with 12-myristate 13-acetate expressed mRNA for CYP4F3 and CYP4F3B. Promoter analysis of the CYP4F3 gene demonstrated that a region (-174/-90) of this gene was important for its promoter activity in the HL60 cells. This is the first report on the distribution of different CYP4F isoforms in leukocytes and their induction in HL60 cells.

The activity of human telomerase in the cells of acute leukaemias

Telomeres are the end fragments of chromosomes formed by a number of non-coding double-stranded TTAGGG repeats in vertebrates. During cell division the number of repeats decreases, leading to cell senescence or apoptosis. In immortal cells, including cancer cells, the telomere length is stable and maintained by, among other factors, telomerase. The aim of the study is to compare telomerase activity in normal lymphocytes and in leukaemic cells. Samples of acute leukaemia cells, HL 60 cell line and the lymphocytes of healthy volunteers were examined. Telomerase analysis was performed using TeloTAGGG Telomerase PCR ELISAplus (Roche). The relative telomerase activities (RTA) in leukaemic and normal cells were analysed. A high level of RTA was observed in leukaemic cells.

Induction of cytochrome CYP4F3A in all-trans-retinoic acid-treated HL60 cells

Cytochrome P-450 CYP4F3A catalyzes the inactivation of leukotriene B(4) by omega-hydroxylation, an activity of which is specifically expressed in human neutrophils. Here, we examined expression of the LTB(4) omega-hydroxylating activity during the differentiation of HL60 cells, an acute promyelocytic leukemia cell line, in the presence of various inducers. Among the inducers used, all-trans-retinoic acid (ATRA) most strongly induces the LTB(4) omega-hydroxylating activity in a dose-dependent manner. The time course of the induction of the omega-hydroxylating activity correlates well with that of the superoxide-generating activity, indicative of cell differentiation. ATRA-treated cell microsomes convert LTB(4) to its 20-hydroxyl derivative under aerobic conditions in the present of NADPH. The reaction is inhibited by carbon monoxide, an inhibitor of cytochrome P-450, and by antibodies raised against NADPH-P-450 reductase. CYP4F3A appears to be responsible for the LTB(4) omega-hydroxylase activity, based on the following observations: expression of the mRNA for CYP4F3A is observed together with the induction of LTB(4) omega-hydroxylating activity in ATRA-treated HL60 cells; and the apparent K(m) values for the omega-hydroxylation of LTB(4) and lipoxin B(4) by ATRA-treated cell microsomes are essentially the same as those of CYP4F3A in human neutrophil microsomes.

Rhein induces apoptosis in HL-60 cells via reactive oxygen species-independent mitochondrial death pathway

Rhein is an anthraquinone compound enriched in the rhizome of rhubarb, a traditional Chinese medicine herb showing anti-tumor promotion function. In this study, we first reported that rhein could induce apoptosis in human promyelocytic leukemia cells (HL-60), characterized by caspase activation, poly(ADP)ribose polymerase (PARP) cleavage, and DNA fragmentation. The efficacious induction of apoptosis was observed at 100 microM for 6h. Mechanistic analysis demonstrated that rhein induced the loss of mitochondrial membrane potential (DeltaPsi(m)), cytochrome c release from mitochondrion to cytosol, and cleavage of Bid protein. Rhein also induced generation of reactive oxygen species (ROS) and the phosphorylation of c-Jun N-terminal kinase (JNK) and p38 kinase. However, these actions seem not to be associated with the apoptosis induction because antioxidants including N-acetyl cysteine (NAC), Tiron, and catalase did not block rhein-induced apoptosis, although they could block the generation of ROS and the phosphorylation of JNK and p38 kinase. Our data demonstrate that rhein induces apoptosis in HL-60 cells via a ROS-independent mitochondrial death pathway.

Promyelocytic HL60 Cells Express NADPH Oxidase and Are Excellent Targets in a Rapid Spectrophotometric Microplate Assay for Extracellular Superoxide

A great number of drugs, toxicants, and growth factors induce the generation of intermediary reactive oxygen species (ROS). The human promyelocytic leukemia HL60 cell line differentiated along the macrophage or neutrophil lineage is a model system that is frequently used for the generation of ROS by various agents. As a primary source of ROS the superoxide anion produced by an enzymatic complex, NADPH oxidase, is well established. The present study shows that nondifferentiated HL60 cells contain NADPH oxidase and can be used as a model for the assessment of oxidant as well as antioxidant compounds. The expression of the multicomponent NADPH oxidase was demonstrated in nondifferentiated HL60 cells at the molecular level by detection of the mRNAs of the components gp91phox, p47phox, and p67phox as well as functionally by phorbol 12-myristate-13-acetate (PMA)-stimulated generation of superoxide, which was susceptible to inhibition by diphenyleneiodonium. The functional assay was performed using the cells in a log growth phase by adapting a standard microplate assay based on the classic superoxide dismutase-inhibitable reduction of cytochrome c. Validation of the microplate assay was carried out both with nonadherent differentiated HL60 cells and the adherent mouse monocyte-macrophage-like RAW 264.7 cell line, as well as with various compounds of oxidant (bleomycin sulfate, cis-diammineplatinum(II), camptothecin, TNF-alpha, IL-1 beta), nonoxidant (4 alpha-PMA, piracetam), and antioxidant (alpha-tocopherol, ascorbic acid) activity. In summary, we established a highly specific, reproducible and--with the aid of the nondifferentiated HL60 cell line--time-saving superoxide microplate assay as a valuable tool for the rapid screening of compounds for oxidative and antioxidative activity.

Induction of apoptosis by takrisodokyeum through generation of hydrogen peroxide and activation of caspase-3 in HL-60 cells

Takrisodokyeum (TRSDY), a Chinese herbal medicine, has been known to exert anti-tumoral activity in Korea. However, its molecular mechanism of action is not understood. In this study, we found that TRSDY induced apoptosis in HL-60 cells as evidenced by both a characteristic ladder pattern of discontinuous DNA fragments and an increase of annexin V+/PI- stained cell population. Our data demonstrated that TRSDY-induced apoptotic cell death was accompanied by activation of caspase-3 and cleavages of its substrates, poly(ADP-ribose) polymerase (PARP) and RhoGDP dissociation inhibitor (RhoGDI-2; also called D4-GDI) in a time- and concentration-dependent manner. Caspase-3 inhibitor, but not caspase-1 inhibitor, prevented TRSDY-induced apoptosis. Furthermore, treatment with TRSDY increased the production of intracellular hydrogen peroxide and pretreatment of cells with anti-oxidants conferred complete protection against hydrogen peroxide generation and subsequent caspase-3 activation. Taken together, these results suggest that TRSDY induces hydrogen peroxide generation, which, in turn, causes activation of caspase-3, degradation of PARP and D4-GDI, and eventually leads to apoptotic cell death.

Tamoxifen inhibits arylamine N-acetyltransferase activity and DNA-2-aminofluorene adduct in human leukemia HL-60 cells

Genetic regulation of acetyl coenzyme A-dependent N-acetyltransferase (NAT)and O-acetyltransferase (OAT) activities may play an important role in the metabolic activation of arylamine chemicals and carcinogens. N-acetylation is thought to be the first step in arylamine metabolism. The enzyme responsible for N-acetylation is called NAT. In this study, synthetic non-steroidal antiestrogen tamoxifen was selected for determining the inhibition of arylamine NAT activity, gene expression (NAT mRNA) and DNA-2-aminofluorene adduct formation in human leukemia HL-60 cell line. The results demonstrated that tamoxifen did not affect the level of NAT mRNA in HL-60 cells. But the results also showed that NAT activity and 2-Aminofluorene-DNA adduct formation in HL-60 cells were inhibited and decreased by tamoxifen in a dose-dependent manner when the doses of tamoxifen up to 100 micro M. We also examined the standard steady-state kinetic analysis, and the data showed that tamoxifen may be an uncompetitive inhibitor to NAT activity in cytosols based on the decrease apparent values of Km and Vmax. This report is the first finding that tamoxifen inhibited human leukemia HL-60 cells NAT activity and DNA-2-aminofluorene on adduct formation.

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.