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)

The aim of this study was to study interactions between stromal bone marrow microenvironment and leukemic cells. We tested the hypothesis that stromal cells prevent apoptosis of AML cells by up-regulating anti-apoptotic proteins in leukemic blasts. In HL-60 and NB-4 cells, serum deprivation- and ara-C-induced apoptosis was diminished when cells were cocultured with murine MS-5 stromal cells (P < 0.02). This effect was reproduced with conditioned medium from MS-5 cells. Cocultivation with stromal cells induced Bcl-2 expression levels, both by PCR analysis and flow cytometry. In primary AML (n = 14), ara-C-induced apoptosis was significantly lower in cells cocultured with MS-5 cells than in controls (P < 0.001). This effect was partially preserved when leukemic cells were separated from stromal cells by a microporous insert (in 5/9 samples, P = 0.04). In addition, Bcl-2 levels were significantly higher in stroma-supported than in control CD34(+) AML cells (P < 0.01). Bcl-X(L) levels were higher in 5/7 samples grown on stromal layers. Of note, in AML patients resistant to induction chemotherapy (n = 6), Bcl-2 increased significantly after cultivation with stromal cells, but no such increase was noted in cells from chemotherapy-sensitive patients. In conclusion, MS-5 stromal cells prevented apoptosis in HL-60 cells and in primary AML blasts via modulation of Bcl-2 family proteins. The observed association of high Bcl-2 expression in stroma-supported AML blasts in vitro with resistance to chemotherapy in vivo suggests that the same mechanisms may be operational in vivo.
Leukemia 2002 Sep
PMID:Stromal cells prevent apoptosis of AML cells by up-regulation of anti-apoptotic proteins. 1220 Jun 86

Bcr-Abl is a constitutively active tyrosine kinase involved in the development and progression of chronic myeloid leukaemia (CML). It has been demonstrated that Bcr-Abl-positive cells can be uniquely resistant to apoptosis induced by different types of stimuli, but the mechanism by which this is achieved is not defined. In this study we have investigated how cells expressing high expression levels of Bcr-Abl may gain resistance to cytotoxic drugs. We have established cell lines expressing low and high expression levels of Bcr-Abl. Cells expressing elevated Bcr-Abl are resistant to cytotoxic drugs. In drug-sensitive 32D-parental and low Bcr-Abl expressing cells, pro-apoptotic Bcl-2 family members, Bax and Bad translocate from the cytosol to the mitochondrion following a cytotoxic insult. In contrast, high Bcr-Abl expression prevents the early translocation of these pro-apoptotic proteins to the mitochondrion, mitochondrial membrane potential is retained and caspases are inactive. We also demonstrate that IL-3 can contribute to drug resistance in low Bcr-Abl expressing cells, however, independent inhibition of IL-3 activated pathways (PI3K/AKT and Jak/STAT) does not sensitise cells to apoptosis. This study demonstrates that the subcellular translocation of Bax and Bad can be regulated by elevated Bcr-Abl expression and this may be a key event in the abrogation of an apoptotic response following a cytotoxic insult.
Leukemia 2002 Sep
PMID:High Bcr-Abl expression prevents the translocation of Bax and Bad to the mitochondrion. 1220 Jun 87

The apoptotic pathway activated by chimeric anti-CD20 monoclonal antibodies (rituximab, IDEC.C2B8) was analyzed using the Burkitt lymphoma cell line Ramos. Crosslinking of CD20 (CD20XL) induced apoptosis in Ramos cells, which involved loss of mitochondrial membrane potential (Deltapsi(m)), the release of cytochrome-c (cyt-c), and activation of caspases-9 and -3. Nevertheless, several lines of evidence showed that the apoptotic outcome did not depend on these events. First, under circumstances where Ramos cells display resistance to either CD95- or B cell receptor (BCR)-induced apoptosis, CD20XL-induced apoptosis was not affected, pointing to a distinct pathway. Second, the broad-spectrum caspase inhibitor zVAD-fmk prevented processing of caspase-9, -3 and PARP as well as DNA fragmentation, but did not block apoptosis as measured by annexin V staining, cell size and membrane integrity. Lastly, Bcl-2 overexpression blocked cyt-c release and the decrease in Deltapsi(m), and completely prevented CD95- or BCR-mediated apoptosis; however, it did not affect CD20XL-induced cell death. We conclude that although CD20XL can initiate the mitochondrial apoptosis pathway, CD20-induced apoptosis does not necessarily require active caspases and cannot be blocked by Bcl-2. Since most chemotherapeutic drugs require the activation of caspases to exert their cytotoxicity, these findings provide an important rationale for the use of CD20 mAbs in chemoresistant malignancies.
Leukemia 2002 Sep
PMID:CD20-induced B cell death can bypass mitochondria and caspase activation. 1220 Jun 88

Bendamustine is a novel cytostatic agent, with activity in non-Hodgkin's lymphomas including B-chronic lymphocytic leukemia (B-CLL). The knowledge about its mode of action, however, is still limited. Here, we investigated the in vitro ability of bendamustine to induce apoptosis on freshly isolated peripheral lymphocytes in B-CLL and analyze the potential underlying mechanisms of action for inducing apoptosis. In CLL cells taken from 37 previously treated and untreated CLL patients, we investigated the influence of bendamustine alone, and in combination with fludarabine, on the induction of apoptosis and changes of Bcl-2 and Bax expression on mRNA and protein level using the RNase protection assay or flow cytometry, respectively. Apoptotic cells were determined with flow cytometry using the fluorescent DNA-binding agent 7-ADD. Using bendamustine alone in concentrations from 1 microg/ml to 50 microg/ml, a dose- and time-dependent manner of cytotoxicity from 30.4% to 94.8% after 48 h could be observed. The LD50 for untreated and pretreated CLL cells was 7.3 or 4.4 microg/ml, respectively. The median apoptotic rate was similar in both groups. The combination of bendamustine with fludarabine led to a highly synergistic effect in inducing apoptosis, which was 150% higher than expected for bendamustine plus fludarabine. The level of the initial Bcl-2 and Bax protein and the m-RNA expression remained unchanged during the incubation with bendamustine. In conclusion, this study demonstrates for the first time the in vitro efficacy of bendamustine in inducing apoptosis in B-CLL cells alone and in combination with fludarabine.
Leukemia 2002 Oct
PMID:In vitro evaluation of bendamustine induced apoptosis in B-chronic lymphocytic leukemia. 1235 63

We have evaluated the role of caspases and the mitochondrial apoptosis inducing-factor (AIF) in apoptosis induced by cladribine (2CdA), in vitro, in cells from patients of B-CLL and in peripheral blood lymphocytes from normal donors. In sensitive B-CLL cells, apoptosis was characterized by cell shrinking, loss of mitochondrial membrane potential (DeltaPsi(m)), phosphatidylserine exposure, activation of caspases 3, 7, 8 and 9, reduction of Mcl-1 levels, translocation of AIF from mitochondria to nucleus and chromatin condensation. No significant variations in the levels of Bcl-2, Bax and Bak proteins were noticed upon treatment with 2CdA. Co-treatment of cells with the pan-caspase inhibitor Z-VAD-fmk attenuated some morphological and biochemical characteristics of apoptosis and delayed 2CdA-induced DeltaPsi(m) loss, but did not prevent cell death. Z-VAD-fmk did not prevent 2CdA-induced AIF translocation but in this case apoptotic cells displayed only peripheral chromatin condensation, characteristic of AIF action. Reduced or negligible caspase 3 expression did not prevent 2CdA toxicity in cells from four patients. Cells from three patients that responded poorly to 2CdA lacked expression of caspases 9 or 3. Cells from another patient resistant to 2CdA expressed caspases 3, 7, 8 and 9 but they were not activated by treatment. These results indicate that execution of apoptosis is carried out independently by AIF and caspases, which are responsible for the development of apoptotic phenotype in response to 2CdA. Although caspases can also collaborate in DeltaPsi(m) loss, proapoptotic proteins from the Bcl-2 superfamily may be the key inducers of DeltaPsi(m) loss and apoptosis in B-CLL cells sensitive to 2CdA.
Leukemia 2002 Oct
PMID:Role of caspases and apoptosis-inducing factor (AIF) in cladribine-induced apoptosis of B cell chronic lymphocytic leukemia. 1235 64

An antisense oligodeoxynucleotide (ODN) complementary to the first six codons of the Bcl-2 mRNA, G3139 (oblimersen sodium; Genasense), has been shown to downregulate Bcl-2 and produce responses in a variety of malignancies including drug-resistant lymphoma. Incubation of ex vivo purified plasma cells from patients with multiple myeloma (MM) with carboxyfluorescein (FAM)-labeled antisense ODNs resulted in a time- and dose-dependent uptake in the cytoplasm and nucleus. No major differences in uptake of Bcl-2 antisense ODNs were observed among patients' samples. Incubation of purified myeloma plasma cells with G3139, but not solvent or reverse polarity control ODNs, resulted in a reduction (>75%) of Bcl-2 mRNA levels after 2 and 4 days, as measured by Real-Time PCR. Treatment with G3139 led to a sequence-specific reduction of Bcl-2 protein levels within 4 days of exposure in 10 out of 11 clinical samples from patients with chemosensitive and multidrug-resistant disease, without significant reduction of alpha-Actin, Bax, Bcl-XL, or Mcl-1 proteins. This resulted in a significantly enhanced sensitivity of the myeloma tumor cells to dexamethasone or doxorubicin-induced apoptosis. G3139 can consistently enter myeloma cells, downregulate the expression of Bcl-2, and enhance the efficacy of myeloma therapy. These data support further clinical evaluation of G3139 therapy in multiple myeloma.
Leukemia 2003 Jan
PMID:Chemosensitization of myeloma plasma cells by an antisense-mediated downregulation of Bcl-2 protein. 1252 80

TRAIL is a member of the tumor necrosis factor superfamily which induces apoptosis in cancer but not in normal cells. Akt1 promotes cell survival and blocks apoptosis. The scope of this paper was to investigate whether a HL60 human leukemia cell clone (named AR) with constitutively active Akt1 was resistant to TRAIL. We found that parental (PT) HL60 cells were very sensitive to a 6 h incubation in the presence of TRAIL and died by apoptosis. In contrast, AR cells were resistant to TRAIL concentrations as high as 2 microg/ml for 24 h. Two pharmacological inhibitors of PI3K, Ly294002 and wortmannin, restored TRAIL sensitivity of AR cells. AR cells stably overexpressing PTEN had lower Akt1 activity and were sensitive to TRAIL. Conversely, PT cells stably overexpressing a constitutive active form of Akt1 became TRAIL resistant. TRAIL activated caspase-8 but not caspase-9 or -10 in HL60 cells. We did not observe a protective effect of Bcl-X(L) or Bcl-2 against the cytotoxic activity of TRAIL, even though TRAIL induced cleavage of BID. There was a close correlation between TRAIL sensitivity and intranuclear presence of the p50 subunit of NF-kappaB. Higher levels of the FLICE inhibitory protein, cFLIP(L), were observed in TRAIL-resistant cells. Both the cell permeable NF-kappaB inhibitor SN50 and cycloheximide lowered cFLIP(L)expression and restored sentivity of AR cells to TRAIL. Our results suggest that Akt1 may be an important regulator of TRAIL sensitivity in HL60 cells through the activation of NF-kappaB and up-regulation of cFLIP(L) synthesis.
Leukemia 2003 Feb
PMID:Constitutively active Akt1 protects HL60 leukemia cells from TRAIL-induced apoptosis through a mechanism involving NF-kappaB activation and cFLIP(L) up-regulation. 1259 38

Neutrophils and monocytes/macrophages are derived from common progenitors, but exhibit markedly different lifespans. Differentiated neutrophils are short-lived and die rapidly by apoptosis, while monocytic cells are longer-lived. In this report we used the HL-60 cell line as a model system to identify differences in apoptotic pathways which might account for the differing lifespans of granulocytic vs monocytic cells. We observed that induction of granulocytic differentiation by retinoic acid led to robust activation of the executioner protease caspase-3, and early onset of apoptosis. By contrast, caspase-3 was not appreciably activated during phorbol 12-myristate 13-acetate (PMA)-induced monocytic differentiation, and apoptosis was delayed in these cells. Since the activation of caspase-3 is inhibited by members of the inhibitor of apoptosis (IAP) and Bcl-2 protein families, we investigated the expression of anti-apoptotic members of these families. Induction of monocytic differentiation led to marked upregulation of the IAP protein XIAP, as well as the Bcl-2 family member Bcl-X(L). During granulocytic differentiation the levels of XIAP progressively declined, while Bcl-X(L) levels remained unchanged. A different IAP protein, survivin, was downregulated during differentiation along either lineage, as was expression of Bcl-2. The upregulation of Bcl-X(L) during monocytic differentiation coincided with phosphorylation/activation of STAT3, a known activator of bcl-X gene transcription. Moreover, Bcl-X(L) upregulation was dependent on MEK/ERK signaling. Upregulation of XIAP proceeded in a MEK/ERK-independent fashion. Treatment with antisense Bcl-X(L) or XIAP oligonucleotides resulted in significant loss of viability in cells differentiating along the monocytic lineage. Together, these findings indicate that the levels of XIAP and Bcl-X(L) are regulated by distinct pathways during monocytic differentiation, and that upregulation of these proteins contributes to the increased longevity of cells in the monocytic lineage.
Leukemia 2003 Feb
PMID:Differential activation of apoptosis regulatory pathways during monocytic vs granulocytic differentiation: a requirement for Bcl-X(L)and XIAP in the prolonged survival of monocytic cells. 1259 39

Minimal residual disease (MRD) cells are thought to be responsible for the persistence and relapse of acute myeloid leukemia (AML). Flow cytometric MRD detection by the establishment of a leukemia-associated phenotype (LAP) at diagnosis can be used in 80% of AML patients, allowing detection and functional characterization of MRD in follow-up bone marrow. One of the mechanisms contributing to inefficient chemotherapy is apoptosis resistance. Measuring apoptosis parameters in MRD cells will help to unravel the importance of apoptosis resistance in AML. We therefore developed a four-color flow cytometry method that enables establishment of apoptosis-related protein expression such as Bcl-2, Bcl-x(L), Mcl-1 and Bax at diagnosis and in MRD. Firstly, validation of this assay using Western blot analysis in five leukemia cell lines showed a significant correlation (R=0.70: P<0.0001). Secondly, the influence of the permeabilization procedure on LAP expression was investigated in 38 AML samples at diagnosis and in 42 MRD samples. Quantification of the frequency of LAP+ cells with and without permeabilization showed no significant differences (diagnosis: P= 0.57, follow-up: P= 0.43). The flow cytometric protocol thus enables analysis of apoptosis-related proteins at different stages of the disease, which will lead to a better understanding of the role of apoptosis resistance in the emergence of MRD in AML.
Leukemia 2003 Apr
PMID:A flow cytometric method to detect apoptosis-related protein expression in minimal residual disease in acute myeloid leukemia. 1268 37

The NF-kappaB2/p100 and bcl-3 genes are involved in chromosomal translocations described in chronic lymphocytic leukemias (CLL) and non-Hodgkin's lymphomas, and nuclear factor kappaB (NF-kappaB) protects cancer cells against apoptosis. Therefore, we investigated whether this transcription factor could modulate the expression of the Bcl-2 antiapoptotic protein. Bcl-2 promoter analysis showed multiple putative NF-kappaB binding sites. Transfection assays of bcl-2 promoter constructs in HCT116 cells showed that NF-kappaB can indeed transactivate bcl-2. We identified a kappaB site located at position -180 that can only be bound and transactivated by p50 or p52 homodimers. As p50 and p52 homodimers are devoid of any transactivating domains, we showed that they can transactivate the bcl-2 promoter through association with Bcl-3. We also observed that stable overexpression of p100 and its processed product p52 can induce endogenous Bcl-2 expression in MCF7AZ breast cancer cells. Finally, we demonstrated that, in breast cancer and leukemic cells (CLL), high NF-kappaB2/p100 expression was associated with high Bcl-2 expression. Our data suggest that Bcl-2 could be an in vivo target gene for NF-kappaB2/p100.
Leukemia 2003 Jul
PMID:NF- kappa B2/p100 induces Bcl-2 expression. 1283 24


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