Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P10415 (Bcl-2)
 33,771 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Activation of protein kinase C (PKC) by TPA in human U937 myeloid leukemia cells is associated with induction of adherence, differentiation, and G0/G1 cell cycle arrest. In this study, we demonstrate that in addition to these differentiating cells about 25% of U937 cells accumulated in the subG1 phase after TPA treatment. This effect proved to be phorbol ester-specific, since other compounds such as retinoic acid or vitamin D3 failed to induce apoptosis in conjunction with differentiation. Only a specific inhibitor of PKC, GF109203X, but not the broad-spectrum kinase inhibitor staurosporine or a tyrosine kinase inhibitor genistein could reverse the induction of apoptosis. Bryostatin-1, another specific PKC activator with distinct biochemical activity failed to induce apoptosis. Moreover, bryostatin-1 completely abolished the induction of apoptosis in U937 cells even if added 8 hours after TPA treatment. Apart from apoptosis induced by various chemotherapeutic drugs, TPA-related cell death is not mediated by an autocrine Fas-FasL loop and could not be prevented by a blocking antibody to the Fas receptor. However, a 75% reduction in the number of apoptotic cells after TPA stimulation was achieved by preincubation with a blocking antibody to the TNFalpha receptor. Tetrapeptide cleavage assays revealed a four-fold increase in the DEVD-cleavage activity in U937 cells compared to a three-fold increase in TUR cells. Immunoblotting demonstrated that TUR cells did not activate significant levels of caspase-3 or -7, whereas in U937 cells a 20-kDa cleavage product corresponding to activated caspase-3 was detectable after 3 d TPA exposure. Moreover, immunoblots revealed a strongly reduced expression of the adaptor molecule APAF-1, which is required for cytochrome c-dependent activation of caspase-9 and subsequently caspase-3. APAF-1 proved to be inducible after PKC activation with phorbol ester in U937, but not in TUR cells. Thus, APAF-1 expression may, at least in part, be regulated by PKC activity and reduced APAF-1 levels are associated with resistance to various inducers of apoptosis. Furthermore, TPA exposure of U937 cells is associated with increased levels of the pro-apoptotic proteins Bak and Bcl-xs, whereas simultaneously a decline in the Bcl-2 expression was noticable.
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PMID:Protein kinase C activation modulates pro- and anti-apoptotic signaling pathways. 1113 46

Glucocorticoid hormones are known to enhance gonadotropin/cAMP-induced steroidogenesis in rat and human granulosa cells. As glucocorticoids induce apoptosis in numerous cell types, we investigated the role of glucocorticoids in the control of apoptosis in immortalized human granulosa cells (HO-23) transfected with a temperature-sensitive mutant of p53 (Val(135)). When HO-23 were incubated with forskolin in the presence or absence of dexamethasone (Dex) at 32 or 37 C, progesterone production was higher by 4- and 8-fold in the presence of Dex at 37 or 32 C, respectively (P: < 0. 01). The expression of adrenodoxin (ADX), which is an intrinsic part of the cytochrome P450 side-chain cleavage enzyme system, remained the same in the presence or absence of Dex in forskolin-stimulated cells. Dex reduced apoptosis (to 33% of control) in cultures after activation of p53 by shifting the temperature from 37 to 32 C. Moreover, Dex suppressed apoptosis induced by serum deprivation (to 40% of control) or forskolin stimulation (to 28% and 40% at 37 and at 32 C, respectively). The protective effect of Dex on cAMP-, p53-, and serum deprivation-induced apoptosis was confirmed by both 4',6-diamido-2-phenylindole hydrochloride DNA staining and terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling with an ED(50) of 7 nM Dex. Hydrocortisone showed a similar antiapoptotic effect. The protective effect of glucocorticoids against apoptosis was completely abolished by RU486 when cells were coincubated with 10 nM Dex and 10-100 nM RU486. The protection against apoptosis by glucocorticoid involved a sharp elevation in intracellular levels of Bcl-2 (3-7.6 fold; P: < 0.01). In contrast to the effect of Dex in the prevention of apoptosis in HO-23 granulosa cells, Dex dramatically stimulated apoptosis by 3-fold in LTR-6 myeloid leukemia cells expressing the same temperature-sensitive mutant (Val(135) p53) and the same amount of glucocorticoid receptor-alpha. Forskolin did not stimulate apoptosis when incubated with these cells. However, it augmented by 1.2-fold the p53-induced apoptosis in cells shifted from 37 to 32 C. Dex further enhanced apoptosis by 1.9-fold in p53-activated cultures (32 C). Incubation of the cells with Dex dramatically reduced Bcl-2 levels to 15% of control at 37 C (P: < 0.01) or 32 C in the presence or absence of forskolin (P: < 0.01). Our data suggest that glucocorticoids exert a protective effect against induced apoptosis in immortalized granulosa cells and a stimulatory effect on apoptosis in myeloid leukemia cells. Moreover, modulation of Bcl-2 levels plays an important role in mediating the glucocorticoid effect on cell survival. The opposite effect of glucocorticoids on Bcl-2 levels in the two cell lines may be due to the different ontogeneses of the two cell types: epithelial for granulosa cells vs. mesenchymal for myeloid cells studied in the present work.
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PMID:Glucocorticoids protect against apoptosis induced by serum deprivation, cyclic adenosine 3',5'-monophosphate and p53 activation in immortalized human granulosa cells: involvement of Bcl-2. 1115 53

The proto-oncogene c-myb is constitutively expressed in murine leukemia virus-induced myeloid leukemia (MML) due to the integration of virus at this locus. Our recent focus has been the determination of genes regulated by this transcription factor that may be involved in transformation. Data presented here, using conditional expression of Myb in myeloid cells, show that c-Myb directly transactivates the endogenous c-myc and Bcl-2 genes, which explains at least in part how c-Myb regulates proliferation and survival. In addition, c-Myb prevents expression at the RNA level of the tumor suppressor INK4b gene. This gene encodes a cyclin-dependent kinase inhibitor, p15INK4b, that is normally upregulated at the mRNA level during myeloid differentiation and promotes growth arrest. The MMLs are generally characterized as differentiated monocytic tumors and possess the phenotype that is normally associated with p15INK4b expression. c-Myb inhibits expression of this gene, however, and therefore acts to promote a pathway which is abnormal in mature cells. This activity of c-Myb collaborates with its maintenance of c-myc expression to promote growth.
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PMID:Three genes with different functions in transformation are regulated by c-Myb in myeloid cells. 1125 71

The role of interferon (IFN)-gamma as a sensitizing agent in apoptosis induced by ligation of death receptors has been evaluated in human myeloid leukemia cells. Incubation of U937 cells with IFN-gamma sensitized these cells to apoptosis induced by tumor necrosis factor-alpha, agonistic CD95 antibody, and tumor necrosis factor-related apoptosis-inducing ligand. Other human myeloid leukemic cells were also sensitized by IFN-gamma to death receptor-mediated apoptosis. Treatment of U937 cells with IFN-gamma up-regulated the expression of caspase-8 and potently synergized with death receptor ligation in the processing of caspase-8 and BID cleavage. Concomitantly, a marked down-regulation of BCL-2 protein was also observed in cells incubated with IFN-gamma. Furthermore, the caspase-dependent generation of a 23-kDa fragment of BCL-2 protein, the release of cytochrome c from mitochondria and the activation of caspase-9 were also enhanced upon death receptor ligation in IFN-gamma-treated cells. Ectopically expressed Bcl-2 protein inhibited IFN-gamma-induced sensitization to apoptosis. In summary, these results indicate that IFN-gamma sensitizes human myeloid leukemic cells to a death receptor-induced, mitochondria-mediated pathway of apoptosis.
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PMID:Interferon-gamma sensitizes human myeloid leukemia cells to death receptor-mediated apoptosis by a pleiotropic mechanism. 1127 36

Bcl-2 belongs to a growing family of proteins which regulates programmed cell death (apoptosis). Overexpression of Bcl-2 has been observed in 70% of breast cancer, 30-60% of prostate cancer, 80% of B-cell lymphomas, 90% of colorectal adenocarcinomas, and many other forms of cancer. Thereby, Bcl-2 is an attractive new anti-cancer target. Herein, we describe the discovery of novel classes of small-molecule inhibitors targeted at the BH3 binding pocket in Bcl-2. The three-dimensional (3D) structure of Bcl-2 has been modeled on the basis of a high-resolution NMR solution structure of Bcl-X(L), which shares a high sequence homology with Bcl-2. A structure-based computer screening approach has been employed to search the National Cancer Institute 3D database of 206 876 organic compounds to identify potential Bcl-2 small-molecule inhibitors that bind to the BH3 binding site of Bcl-2. These potential Bcl-2 small-molecule inhibitors were first tested in an in vitro binding assay for their potency in inhibition of the binding of a Bak BH3 peptide to Bcl-2. Thirty-five potential inhibitors were tested in this binding assay, and seven of them were found to have a binding affinity (IC(50) value) from 1.6 to 14.0 microM. The anti-proliferative activity of these seven active compounds has been tested using a human myeloid leukemia cell line, HL-60, which expresses the highest level of Bcl-2 protein among all the cancer cell lines examined. Compound 6 was the most potent compound and had an IC(50) value of 4 microM in inhibition of cell growth using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Five other compounds had moderate activity in inhibition of cell growth. Compound 6 was further evaluated for its ability to induce apoptosis in cancer cells. It was found that 6 induces apoptosis in cancer cells with high Bcl-2 expression and its potency correlates with the Bcl-2 expression level in cancer cells. Furthermore, using NMR methods, we conclusively demonstrated that 6 binds to the BH3 binding site in Bcl-X(L). Our results showed that small-molecule inhibitors of Bcl-2 such as 6 modulate the biological function of Bcl-2, and induce apoptosis in cancer cells with high Bcl-2 expression, while they have little effect on cancer cells with low or undetectable levels of Bcl-2 expression. Therefore, compound 6 can be used as a valuable pharmacological tool to elucidate the function of Bcl-2 and also serves as a novel lead compound for further design and optimization. Our results suggest that the structure-based computer screening strategy employed in the study is effective for identifying novel, structurally diverse, nonpeptide small-molecule inhibitors that target the BH3 binding site of Bcl-2.
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PMID:Discovery of small-molecule inhibitors of Bcl-2 through structure-based computer screening. 1172 79

It has been shown that the novel synthetic triterpenoid CDDO inhibits proliferation and induces differentiation and apoptosis in myeloid leukemia cells. In the current study the effects of the C-28 methyl ester of CDDO, CDDO-Me, were analyzed on cell growth and apoptosis of leukemic cell lines and primary acute myelogenous leukemia (AML). CDDO-Me decreased the viability of leukemic cell lines, including multidrug resistant (MDR)-1-overexpressing, p53(null) HL-60-Dox and of primary AML cells, and it was 3- to 5-fold more active than CDDO. CDDO-Me induced a loss of mitochondrial membrane potential, induction of caspase-3 cleavage, increase in annexin V binding and DNA fragmentation, suggesting the induction of apoptosis. CDDO-Me induced pro-apoptotic Bax protein that preceded caspase activation. Furthermore, CDDO-Me inhibited the activation of ERK1/2, as determined by the inhibition of mitochondrial ERK1/2 phosphorylation, and it blocked Bcl-2 phosphorylation, rendering Bcl-2 less anti-apoptotic. CDDO-Me induced granulo-monocytic differentiation in HL-60 cells and monocytic differentiation in primary cells. Of significance, colony formation of AML progenitors was significantly inhibited in a dose-dependent fashion, whereas normal CD34(+) progenitor cells were less affected. Combinations with ATRA or the RXR-specific ligand LG100268 enhanced the effects of CDDO-Me on cell viability and terminal differentiation of myeloid leukemic cell lines. In conclusion, CDDO-Me is an MDR-1- and a p53-independent compound that exerts strong antiproliferative, apoptotic, and differentiating effects in myeloid leukemic cell lines and in primary AML samples when given in submicromolar concentrations. Differential effects of CDDO-Me on leukemic and normal progenitor cells suggest that CDDO-Me has potential as a novel compound in the treatment of hematologic malignancies.
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PMID:Novel triterpenoid CDDO-Me is a potent inducer of apoptosis and differentiation in acute myelogenous leukemia. 1175 88

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.
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PMID: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. 1178 77

MK 886, an arachidonic acid-related analog which inhibits the enzyme, 5-lipoxygenase by an indirect mechanism involving the 5-lipoxygenase activating protein, rapidly increased U937 cytosol Ca(2+), much of which localized around the cell nuclei. Five-lipoxygenase activity was not directly involved since the direct redox-dependent 5-LPOx inhibitor, SC-41661A did not increase Ca(2+). U937 cells subsequently undergo classic type 1 programmed cell death. At least initially the ionized calcium originates from internal stores. Coincident with the rise in U937 ionized calcium, MK 886 rapidly increased reactive oxygen species and reduced mitochondrial membrane potential, as judged by several fluorescent probes. The Ca(2+) response of myeloid leukemia-derived HL-60 cells to MK 886 was similar and both cell lines express Bcl-2 protein. Bcl-2-negative Panc-1 and PC-3 cells did not respond to MK 886 with a Ca(2+) signal but did develop oxidative stress and a decline in mitochondrial membrane potential; these events are thought to contribute to the inhibition of cell proliferation and induction of a type 2 PCD. In addition to its marked inhibition of Bcl-2 mRNA synthesis, an interesting hypothesis is that MK 886, serving as a low molecular weight ligand, either by direct or indirect inhibition of U937 Bcl-2 protein function, possibly related to an ion channel activity, alters the distribution of intracellular, possibly nuclear Ca(2+), thereby promoting the development of type 1 programmed cell death.
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PMID:Increased cytosol Ca(2+) and type 1 programmed cell death in Bcl-2-positive U937 but not in Bcl-2-negative PC-3 and Panc-1 cells induced by the 5-lipoxygenase inhibitor MK 886. 1205 16

Interactions between the histone deacetylase inhibitor sodium butyrate (SB) and phorbol 12-myristate 13-acetate (PMA) were examined in human myeloid leukemia cells (U937 and HL-60). Exposure of U937 cells to 1 mM SB and 1 nM PMA (24 h) markedly induced caspase activation and apoptosis, events accompanied by impaired differentiation induction (e.g., reduced plastic adherence and diminished expression of CD11b) as well as reduced clonogenic survival. The PKC inhibitor GF109203X blocked SB-/PMA-mediated apoptosis. Comparable results were obtained in HL-60 cells. Apoptosis was associated with early procaspase 8 activation and Bid cleavage, accompanied by pronounced mitochondrial damage (e.g., loss of mitochondrial membrane potential (DeltaPsi(m)) and cytochrome c release). Neutralization of endogenous TNFalpha by a human soluble TNF receptor substantially blocked SB-/PMA-induced cytochrome c release and apoptosis. Consistent with this, ectopic expression of a mutant dominant-negative caspase 8 or CrmA resulted in a significant decrease in SB-/PMA-induced apoptosis, whereas Bcl-2 overexpression did not. SB/PMA treatment also triggered a decline in the S and G(2)M populations, and dephosphorylation of p34(cdc2). These results indicate that SB interacts with low concentrations of PMA to induce apoptosis in human leukemia cells and that this process proceeds through a PKC-/TNFalpha-dependent pathway in which procaspase 8 and Bid activation play key roles.
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PMID:The histone deacetylase inhibitor sodium butyrate interacts synergistically with phorbol myristate acetate (PMA) to induce mitochondrial damage and apoptosis in human myeloid leukemia cells through a tumor necrosis factor-alpha-mediated process. 1206 15

The effects of the PKC activator and down-regulator bryostatin 1 and the PKC and Chk1 inhibitor 7-hydroxystaurosporine (UCN-01) were compared with respect to potentiation of 1-beta-D-arabinofuranosylcytosine (ara-C)-induced apoptosis in human myelomonocytic leukemia cells (U937). Whereas bryostatin 1 and UCN-01 both markedly enhanced ara-C-induced mitochondrial injury (e.g., cytochrome c and Smac/DIABLO release, loss of mitochondrial membrane potential), caspase activation, and apoptosis, ectopic expression of an N-terminal loop-deleted Bcl-2 mutant protein protected cells from ara-C/UCN-01- but not ara-C/bryostatin 1-mediated lethality. Conversely, ectopic expression of CrmA or dominant-negative caspase-8 abrogated potentiation of ara-C-mediated apoptosis by bryostatin 1 but not by UCN-01. Exposure of cells to ara-C and bryostatin 1 (but not UCN-01) resulted in sustained release of tumor necrosis factor (TNF) alpha; moreover, potentiation of ara-C lethality by bryostatin 1 (but not by UCN-01) was reversed by coadministration of TNF soluble receptors or the selective PKC inhibitor bisindolylmaleimide (1 microM). Finally, similar events were observed in the human promyelocytic leukemia cell line HL-60. Together, these findings suggest that potentiation of ara-C lethality in human myeloid leukemia cells by bryostatin 1 but not UCN-01 involves activation of the extrinsic, receptor-mediated apoptotic pathway, and represents a consequence of bryostatin 1-mediated release of TNF-alpha. They also argue that the mechanism by which bryostatin 1 promotes ara-C-induced mitochondrial injury, caspase activation, and apoptosis involves factors other than or in addition to PKC down-regulation or modulation of Bcl-2 phosphorylation status.
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PMID:Bryostatin 1 and UCN-01 potentiate 1-beta-D-arabinofuranosylcytosine-induced apoptosis in human myeloid leukemia cells through disparate mechanisms. 1248 56


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