Bcl-xL anti-apoptotic network is dispensable for development and maintenance of CML but is required for disease progression where it represents a new therapeutic target (original) (raw)
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Cell growth & differentiation : the molecular biology journal of the American Association for Cancer Research, 1996
Human chronic myelogenous leukemia-blast crisis K562 cells have been demonstrated to be relatively resistant to antileukemic drug-induced apoptosis. This has been attributed to the activity of p210bcr-abl tyrosine kinase present in the K562 cells, which is known to suppress drug-induced apoptosis. Recently, K562 cells have been shown to express the antiapoptosis Bcl-xL but not Bcl-2 proteins. To investigate the contribution of Bcl-xL toward resistance to drug-induced apoptosis, we created K562/Bcl-xS and K562/neo cells by electroporating the expression plasmids pSFFVneo-Bcl-xS and pSFFVneo, containing the bcl-xS and neomycin resistance genes, respectively, into K562 cells. K562/Bcl-xS but not K562/neo cells expressed the bcl-xS mRNA and p19Bcl-xS protein. In contrast, both cell types expressed equivalent levels of Bcl-xL, Bax, Bcl-2, Myc, retinoblastoma, p21cbor-abl, and p145abl proteins. A significant increase in the hemoglobin levels was observed in the K562/Bcl-xS compared with t...
Leukemia, 2001
A characteristic feature of chronic myeloid leukaemia (CML) is the inevitable advancement from a treatable chronic phase to a fatal, drug-resistant stage referred to as blast crisis. The molecular mechanisms responsible for this disease transition remain unknown. As increased expression of Bcr-Abl has been associated with blast crisis CML, we have established transfectants in 32D cells that express low and high levels of Bcr-Abl, and assessed their drug sensitivity. Cells with high Bcr-Abl expression levels are resistant to conventional cytotoxic drugs, and also require higher levels of STI571 (an inhibitor of Bcr-Abl), to induce cell death. Co-treatment with cytotoxic drugs and STI571 increased the sensitivity of the drug-resistant cells. Despite the drug-resistant phenotype, high Bcr-Abl levels concomitantly increased the expression of p53, p21, Bax and down-regulated Bcl-2. These cells maintain a survival advantage irrespective of a reduced proportion of cycling cells and the pro-apoptotic shift in gene expression. In addition, the level of Bcr-Abl expression (high or low) does not alter the growth factor independence and elevated Bcl-xL expression observed. Our study indicates that drug resistance can be primarily attained by increased Bcr-Abl expression, and highlights the potential of therapy which combines STI571 with conventional cytotoxic drugs.
British Journal of Haematology, 2002
In acute myeloid leukaemia (AML), cell kinetic quiescence has been postulated to contribute to drug resistance. As the anti-apoptotic genes Bcl-2 and Bcl-X L have been implicated in cell cycle regulation, we investigated the expression of these genes in non-proliferating (Q) and proliferating (P) AML and normal CD34 + progenitor cells. Using reverse transcription polymerase chain reaction, Bcl-X L and Bcl-2 were overexpressed in Q versus P AML cells, whereas no difference in Bcl-X S and Bax expression was found. Furthermore, the Bcl-X L /X S but not the Bcl-2/Bax ratio was higher in Q AML compared with normal CD34 + Q cells (P ¼ 0AE001). An inverse correlation between Bcl-2 expression of leukaemic Q cells and their ability to enter the cell cycle was found. Treatment with all-trans retinoic acid (ATRA) reduced Bcl-2 and Bcl-X L expression in the leukaemic Q cells, and enhanced their chemosensitivity to cytosine arabinoside (ara-C). These findings demonstrate overexpression of the anti-apoptotic proteins Bcl-X L and Bcl-2 in quiescent CD34 + AML cells and suggest their involvement in the chemoresistance. The observed inverse correlation between Bcl-2 and proliferation suggests a role for Bcl-2 in the cell cycle regulation of AML. These findings could be used in the development of therapies that selectively induce apoptosis in quiescent leukaemic progenitor cells.
Leukemia, 2012
Despite being highly effective for newly diagnosed chronic myeloid leukemia (CML), imatinib not only is inactive against quiescent CML stem cells, but also has limited activity against blast crisis (BC) CML. The relative activity of Bcr-Abl and the expression levels of antiapoptotic proteins in proliferating and quiescent CD34 + BC CML progenitor cells and the effects of targeting antiapoptotic proteins in these cells are unknown. Here we report higher levels of p-CrkL in quiescent than in proliferating CD34 + progenitor cells and comparable expression levels of Bcl-2, Bcl-xL, Mcl-1, and XIAP in the two populations in BC CML. Inhibition of Bcl-2/Bcl-xL by ABT-737 in cells from patients with tyrosine kinase inhibitor (TKI)-resistant BC CML promoted apoptosis in quiescent CD34 + progenitor cells with an efficacy similar to that in proliferating cells. Combination of ABT-737 with imatinib (which decreases Mcl-1 levels) or triptolide (which decreases Mcl-1 and XIAP) synergistically induced death of both proliferating and quiescent CD34 + progenitor cells obtained from TKI-resistant BC CML patients. These results suggest that antiapoptotic proteins are critical targets in BC CML and that activation of apoptosis signaling can eliminate both proliferating and quiescent CD34 + progenitor cells in BC CML, independent of response to TKIs.
Loss of Bcl-x in Ph+ B-ALL increases cellular proliferation and does not inhibit leukemogenesis
Blood, 2008
The kinase inhibitors imatinib mesylate and dasatinib are the preferred treatment for Philadelphia chromosome–positive (Ph+) leukemias, and they are highly successful in the chronic phase of chronic myeloid leukemia (CML). However, they are not efficient in Ph+ B-cell acute lymphoblastic leukemia (B-ALL). Ph+ leukemia cells are highly resistant to apoptosis, and evidence from cell lines and primary cells suggest Bcl-xL as a critical mediator of resistance to apoptosis: however, this concept has never been rigorously tested in an animal model. To clarify the role of Bcl-xL in Ph+ B-ALL, we generated 2 mouse models. In the first model, Ph+ B-ALL and loss of Bcl-xL expression are coinduced; in the second model, leukemia is induced with expression of Bcl-xL protein well above the levels found in wild-type lymphoblasts. Deletion of Bcl-xL did not inhibit leukemogenesis or affect apoptosis, but increased cellular proliferation. Consistent with this result, overexpression of Bcl-xL led to ...
Leukemia stem cells in a genetically defined murine model of blast-crisis CML
Blood, 2007
Myeloid leukemia arises from leukemia stem cells (LSCs), which are resistant to standard chemotherapy agents and likely to be a major cause of drug-resistant disease and relapse. To investigate the in vivo properties of LSCs, we developed a mouse model in which the biologic features of human LSCs are closely mimicked. Primitive normal hematopoietic cells were modified to express the BCR/ABL and Nup98/HoxA9 translocation products, and a distinct LSC population, with the aberrant immunophenotype of lineage−, Kit+/−, Flt3+, Sca+, CD34+, and CD150−, was identified. In vivo studies were then performed to assess the response of LSCs to therapeutic insult. Treatment of animals with the ABL kinase inhibitor imatinib mesylate induced specific modulation of blasts and progenitor cells but not stem- cell populations, thereby recapitulating events inferred to occur in human chronic myelogenous leukemia (CML) patients. In addition, challenge of leukemic mice with total body irradiation was selec...
Apoptosis induces Bcl-XS and cleaved Bcl-XL in chronic lymphocytic leukaemia
Biochemical and Biophysical Research Communications, 2011
The Bcl-X gene has both pro-survival, Bcl-X L , and pro-apoptotic, Bcl-X S , gene products, which are produced by alternative splicing. The function of these proteins has previously been characterised in cell lines, often by transfecting expression constructs, and primary cell systems capable of dynamically regulating Bcl-X L and Bcl-X S have not been described. Such a system is potentially important to allow testing of agents that promote apoptosis by increasing the amount of Bcl-X S at the expense of Bcl-X L. In this report we characterise Bcl-X gene products in primary human leukaemic B-cells in culture conditions associated with survival and apoptosis. We found that Bcl-X S was induced in spontaneous and druginduced apoptosis and that apoptosis induced in cells cultured on mouse fibroblasts expressing CD40 ligand with IL-4 (CD154/IL-4), a condition mimicking the tissue microenvironment, additionally produced expression of cleavage products of Bcl-X L. Both Bcl-X S and Bcl-X L were produced in a caspase dependent manner. We tested emetine, an agent previously reported to increase Bcl-X S but found that it did not have this effect in primary human B-cells. Therefore, there are two mechanisms-cleavage of Bcl-X L and production of Bcl-X S-by which Bcl-X gene products could enhance apoptosis in CLL but neither appeared to have a primary role in inducing leukaemic cell death.
Blood, 2013
Myelodysplastic syndrome (MDS) transforms into an acute myelogenous leukemia (AML) with associated increased bone marrow (BM) blast infiltration. Using a transgenic mouse model, MRP8[NRASD12/hBCL-2], in which the NRAS:BCL-2 complex at the mitochondria induces MDS progressing to AML with dysplastic features, we studied the therapeutic potential of a BCL-2 homology domain 3 mimetic inhibitor, ABT-737. Treatment significantly extended lifespan, increased survival of lethally irradiated secondary recipients transplanted with cells from treated mice compared with cells from untreated mice, with a reduction of BM blasts, Lin-/Sca-1(+)/c-Kit(+), and progenitor populations by increased apoptosis of infiltrating blasts of diseased mice assessed in vivo by technicium-labeled annexin V single photon emission computed tomography and ex vivo by annexin V/7-amino actinomycin D flow cytometry, terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling, caspase 3 cleavage, and re-localization of the NRAS:BCL-2 complex from mitochondria to plasma membrane. Phosphoprotein analysis showed restoration of wild-type (WT) AKT or protein kinase B, extracellular signal-regulated kinase 1/2 and mitogen-activated protein kinase patterns in spleen cells after treatment, which showed reduced mitochondrial membrane potential. Exon specific gene expression profiling corroborates the reduction of leukemic cells, with an increase in expression of genes coding for stem cell development and maintenance, myeloid differentiation, and apoptosis. Myelodysplastic features persist underscoring targeting of BCL-2-mediated effects on MDS-AML transformation and survival of leukemic cells.
Amplification of BCR–ABL and t(3;21) in a patient with blast crisis of chronic myelogenous leukemia
Cancer Genetics and Cytogenetics, 2008
The Philadelphia (Ph) chromosome, or t(9;22), is the hallmark of chronic myelogenous leukemia (CML). It results in juxtaposition of the 5′ part of the BCR gene on chromosome 22 to the 3′ part of the ABL1 gene (previously ABL) on chromosome 9. CML is clinically characterized by three distinct phases: chronic, accelerated, and blast phase. Blast crisis is characterized by the rapid expansion of a population of differentiation arrested blast cells (myeloid or lymphoid cells population), with secondary chromosomal abnormalities present. We report a case of myeloid blast crisis of CML resistant to imatinib mesylate and chemotherapy. By use of cytogenetic, fluorescence in situ hybridization, and comparative genomic hybridization methods, we identified a cluster of BCR–ABL amplification on inverted duplication of the Ph chromosome with t(3;21)(q26;q22) and increased genomic levels of the RUNX1 gene (previously AML1). The t(3;21)(q26;q22) is a recurrent chromosomal abnormality in some cases of CML blast phase and in treatment-related myelodysplastic syndrome and acute myeloid leukemia. Amplification or copy number increase of RUNX1 has been reported in childhood acute lymphoblastic leukemia. Our study indicated that the progenitor of CML was BCR–ABL dependent through the amplification of Ph chromosome as a mechanism of resistance to imatinib therapy. The coexistence of BCR–ABL and t(3;21)(q26;q22) with RUNX1 rearrangement might play a pivotal role in the CML blast transformation.