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PubMed2006

Arf gene loss enhances oncogenicity and limits imatinib response in mouse models of Bcr-Abl-induced acute lymphoblastic leukemia.

Mouse bone marrow cells transduced with retroviral vectors encoding either of two oncogenic Bcr-Abl isoforms (p210(Bcr-Abl) and p185(Bcr-Abl)) induce B cell lympholeukemias when transplanted into lethally irradiated mice. If the activity of the Arf tumor suppressor is compromised, these donor cells initiate a much more highly aggressive and rapidly fatal disease. When mouse bone marrow cells expressing Bcr-Abl are placed in short-term cultures selectively designed to support the outgrowth of pre-B cells, only those lacking one or two Arf alleles can initiate lympholeukemias when inoculated into immunocompetent, syngeneic recipient mice. Although the ABL kinase inhibitor imatinib mesylate (Gleevec) provides highly effective treatment for BCR-ABL-positive chronic myelogenous leukemia, it has proven far less efficacious in the treatment of BCR-ABL-positive acute lymphoblastic leukemias (ALLs), many of which sustain deletions of the INK4A-ARF (CDKN2A) tumor suppressor locus. Mice receiving Arf-/- or Arf+/- p210(Bcr-Abl)-positive pre-B cells do not achieve remission when maintained on high doses of oral imatinib therapy and rapidly succumb to lympholeukemia. Although cells expressing the Bcr-Abl kinase can proliferate in the absence of IL-7, they remain responsive to this cytokine, which can reduce their sensitivity to imatinib. Treatment of Arf-/-, p210(Bcr-Abl)-positive pre-B cells with imatinib together with an inhibitor of JAK kinases abrogates this resistance, suggesting that this combination may prove beneficial in the treatment of BCR-ABL-positive acute lymphoblastic leukemia.

Alleles↗

PubMed2002

Leading prognostic relevance of the BCR-ABL translocation in adult acute B-lineage lymphoblastic leukemia: a prospective study of the German Multicenter Trial Group and confirmed polymerase chain reaction analysis.

The BCR-ABL fusion, the molecular equivalent of the Philadelphia translocation, gains importance for treatment stratification in adult acute lymphoblastic leukemia (ALL). In this prospective study, samples from 478 patients with CD10(+) B-cell precursor ALL (c-ALL and pre-B ALL) underwent BCR-ABL reverse transcription-polymerase chain reaction (RT-PCR) analysis with double testing of positive samples. Patients were stratified according to the PCR result and treated in 2 German Multicenter Trials of Adult ALL. The outcome was followed and the prognostic impact of BCR-ABL was compared to clinical risk features. Of the 478 samples, 432 had an evaluable BCR-ABL result. Thirty-seven percent of the c-ALL and pre-B ALL patients were BCR-ABL(+) (p190, 77%; p210, 20%; simultaneous p190/p210, 3%). BCR-ABL positivity was associated with the high-risk features of older age (45 years versus 30 years median age; P =.0001) and higher white blood cell counts (23 500/microL versus 11 550/microL; P =.0001). Univariate and multivariate analyses revealed BCR-ABL as the leading factor for a poor prognosis (P =.0001) in comparison to clinical risk criteria. Irrespective of the breakpoint, presence of any BCR-ABL transcript predicted a lower chance of initial treatment response (68.4% versus 84.6%; P =.001) and a lower probability of disease-free survival at 3 years (0.13 versus 0.47; P =.0001). This bad outcome was not influenced by postinduction high-dose treatment stratifications. The results show a high prevalence of BCR-ABL fusion transcripts with predominance of p190. BCR-ABL RT-PCR is confirmed as a sensitive, rapid method to diagnose t(9;22), and p190 and p210 are unequivocally demonstrated as the most important predictors of poor long-term survival despite intensified chemotherapy.

Adolescent↗

PubMed2006

Imatinib mesylate minimally affects bcr-abl+ and normal monocyte-derived dendritic cells but strongly inhibits T cell expansion despite reciprocal dendritic cell-T cell activation.

In chronic myeloid leukemia, bcr-abl+ monocytes provide a unique opportunity to generate dendritic cells (DC) expressing a broad spectrum of leukemic antigens, and bcr-abl+ DC vaccines may allow immunological eradication of leukemic cells persisting under treatment with the tyrosine kinase inhibitor imatinib. However, the efficiency of bcr-abl+ DC vaccines will critically depend on the absence of deleterious effects of bcr-abl and of imatinib on DC functions. We show that bcr-abl+ monocytes, devoid of contamination of CD14low granulocytic precursors, differentiate into DC with typical immunophenotypical and functional features, and bcr-abl transcription decreases simultaneously. During differentiation, imatinib induces a slight increase of DC apoptosis and prevents CD1a up-regulation in a dose-dependent manner in bcr-abl+ and normal monocyte-derived DC, but at most, 25% of DC fail to acquire CD1a. When DC maturation is induced in the presence of imatinib, bcr-abl+ and normal monocyte-derived DC up-regulate major histocompatibility complex and costimulatory molecules, CC chemokine receptor 7 and CD83. However, secretion of interleukin-12p70 is decreased in a dose-dependent manner. Imatinib exposure of bcr-abl+ and normal monocyte-derived DC during differentiation and maturation is not detrimental to T cell immunostimulatory functions of DC. In sharp contrast, imatinib, when added to DC-T cell cultures, profoundly suppresses DC-mediated T cell proliferation, despite reciprocal DC-T cell activation attested by up-regulation of CD25 on T cells and of CD86 on DC. Our findings demonstrate that T cells, not normal or bcr-abl+ monocyte-derived DC, are major targets for imatinib immunomodulatory effects. It can be envisioned already that imatinib-free windows will be required to enable vaccination-induced, leukemia-specific T cell expansion.

Adult↗

PubMed2000

Selection and characterization of BCR-ABL positive cell lines with differential sensitivity to the tyrosine kinase inhibitor STI571: diverse mechanisms of resistance.

Targeting the tyrosine kinase activity of Bcr-Abl with STI571 is an attractive therapeutic strategy in chronic myelogenous leukemia (CML). A few CML cell lines and primary progenitors are, however, resistant to this compound. We investigated the mechanism of this resistance in clones of the murine BaF/3 cells transfected with BCR-ABL and in 4 human cell lines from which sensitive (s) and resistant (r) clones were generated by various methods. Although the resistant cells were able to survive in the presence of STI571, their proliferation was approximately 30% lower than that of their sensitive counterparts in the absence of the compound. The concentration of STI571 needed for a 50% reduction in viable cells after a 3-day exposure was on average 10 times higher in the resistant (2-3 micromol/L) than in the sensitive (0.2-0.25 micromol/L) clones. The mechanism of resistance to STI571 varied among the cell lines. Thus, in Baf/BCR-ABL-r, LAMA84-r, and AR230-r, there was up-regulation of the Bcr-Abl protein associated with amplification of the BCR-ABL gene. In K562-r, there was no Bcr-Abl overexpression, but the IC(50) for the inhibition of Bcr-Abl autophosphorylation was increased in the resistant clones. Sequencing of the Abl kinase domain revealed no mutations. The multidrug resistance P-glycoprotein (Pgp) was overexpressed in LAMA84-r, indicating that at least 2 mechanisms of resistance operate in this cell line. KCL22-r showed neither Bcr-Abl up-regulation nor a higher threshold for tyrosine kinase inhibition by STI571. We conclude that BCR-ABL-positive cells can evade the inhibitory effect of STI571 by different mechanisms, such as Bcr-Abl overexpression, reduced intake mediated by Pgp, and, possibly, acquisition of compensatory mutations in genes other than BCR-ABL.

Antineoplastic Agents↗

PubMed1989

No correlation between locations of bcr breakpoints and clinical states in Ph1-positive CML patients.

The majority of patients with chronic myelogenous leukemia (CML) have a characteristic reciprocal translocation between chromosome 9 and 22, resulting in the Philadelphia (Ph1) chromosome. During this translocation, the c-abl oncogene on chromosome 9 is transferred to the Ph1 chromosome and linked to a breakpoint cluster region (bcr), which is part of a large bcr gene. This phenomenon results in the formation of a bcr-c-abl fusion gene, which is transcribed into an 8.5 kb chimeric mRNA encoding a 210 kd bcr-c-abl fusion protein. The fusion protein has tyrosine kinase activity implicated in the pathogenesis of CML. The breakpoint near the c-abl locus on chromosome 9 can occur within a large area. In contrast, the breakpoints on chromosome 22 cluster within the bcr region of 5.8 kb. A chronic phase lasts for an average of 2 to 3 years; and, subsequently, most patients enter blast crisis. In the present study, we examined 15 Ph1-positive CML patients (eight in chronic phase, one in accelerated phase, and six in blast crises) as to whether the identifiable difference in the locations of the bcr breakpoints exist between CML patients in chronic phase and those in blast crisis. In seven of eight CML patients in chronic phase, in one in accelerated phase, and in four out of six CML patients in blast crisis, the bcr breakpoints clustered in the 3' portion of the bcr. Thus, we could not find out the correlation between the locations of the bcr breakpoints and the clinical stage of the CML patients. This might imply that blastic transformation in Ph1-positive CML was caused by other mechanisms than the transition of the bcr breakpoints.

Blast Crisis↗

PubMed1994

Detection of chimeric BCR-ABL genes on bone marrow samples and blood smears in chronic myeloid and acute lymphoblastic leukemia by in situ hybridization.

The presence of BCR-ABL fusion genes has important diagnostic and prognostic implications in chronic myeloid leukemia (CML) and acute lymphoblastic leukemia (ALL). The CML-specific chimeric BCR-ABL gene with a break involving the major breakpoint cluster region (M-bcr) of the BCR-gene has been detected by means of fluorescence in situ hybridization (FISH). In this study, we present a FISH protocol that allows the detection of breaks in both the major and the minor breakpoint cluster region (m-bcr). Three hybridization signals of D107F9, a yeast artificial chromosome (YAC)-derived probe spanning the breakpoint regions of the BCR gene, were indicative of the translocation events. To increase the specificity further, this probe was combined with cos-abl 8, a cosmid probe flanking the breakpoint within the ABL gene for dual-color hybridization. Samples of 21 patients with CML, the ALL-derived cell line SUP-B15, and of seven patients with Philadelphia chromosome (Ph1)-positive ALL (three of them with breakpoints within m-bcr) were examined. BCR-ABL fusion was detected in all cases with high specificity (false-positive nuclei: mean, 0.1%). On cytogenetic preparations, the percentages of BCR-ABL-positive interphase cells ranged from 53% to 91%. Comparable efficiencies were achieved on blood smears. In conclusion, hybridization with D107F9 and cos-abl 8 allows unambiguous diagnosis of BCR-ABL genes and is likely to become an important tool for the monitoring of therapies in patients with CML and ALL.

Adult↗

PubMed1993

Philadelphia negative, BCR-ABL positive adult acute lymphoblastic leukemia (ALL) in 2 of 39 patients with combined cytogenetic and molecular analysis.

We performed cytogenetic and molecular analysis of the BCR-ABL rearrangement by polymerase chain reaction (PCR) in 39 consecutive cases of adult acute lymphoblastic leukemia (ALL). Eleven patients had a Philadelphia (Ph) chromosome. Thirteen patients had a BCR-ABL rearrangement, involving minor breakpoint cluster region (m-bcr, situated in intron 1 of the BCR gene) in 11 cases, and major breakpoint cluster region (M-bcr, 'specific' of chronic myeloid leukemia) in the remaining two cases. All of the 12 BCR-ABL cases studied immunologically were of early B, CALLA-positive immunophenotype. The 13 BCR-ABL positive cases included the 11 Ph-positive cases, and two patients with normal karyotype at diagnosis. In the two Ph-negative BCR-positive cases, seven (patient 1) and 18 (patient 2) mitoses had been examined at diagnosis. In patient 1, Ph negativity at diagnosis could certainly be explained by the small number of mitoses analyzed, as a Ph chromosome was found at relapse. This was less probable in patient 2, who raised the issue of whether authentic Ph-negative BCR-ABL-positive ALL exists (as in the chronic myeloid leukemia model) or not. Whatever the explanation, our results suggest that molecular detection of BCR-ABL should be more widely used in B-lineage ALL.

Adult↗

PubMed1997

Distribution of ABL and BCR genes in cell nuclei of normal and irradiated lymphocytes.

Using dual-color fluorescence in situ hybridization (FISH) combined with two-dimensional (2D) image analysis, the locations of ABL and BCR genes in cell nuclei were studied. The center of nucleus-to-gene and mutual distances of ABL and BCR genes in interphase nuclei of nonstimulated and stimulated lymphocytes as well as in lymphocytes stimulated after irradiation were determined. We found that, after stimulation, the ABL and BCR genes move towards the membrane, their mutual distances increase, and the shortest distance between heterologous ABL and BCR genes increases. The distribution of the shortest distances between ABL and BCR genes in the G0 phase of lymphocytes corresponds to the theoretical distribution calculated by the Monte-Carlo simulation. Interestingly, the shortest ABL-BCR distances in G1 and S(G2) nuclei are greater in experiment as compared with theory. This result suggests the existence of a certain regularity in the gene arrangement in the G1 and S(G2) nuclei that keeps ABL and BCR genes at longer than random distances. On the other hand, in about 2% to 8% of lymphocytes, the ABL and BCR genes are very close to each other (the distance is less than approximately 0.2 to 0.3 microm). For comparison, we studied another pair of genes, c-MYC and IgH, that are critical for the induction of t(8;14) translocation that occurs in the Burkitt's lymphoma. We found that in about 8% of lymphocytes, c-MYC and IgH are very close to each other. Similar results were obtained for human fibroblasts. gamma-Radiation leads to substantial changes in the chromatin structure of stimulated lymphocytes: ABL and BCR genes are shifted to the nuclear center, and mutual ABL-BCR distances become much shorter in the G1 and S(G2) nuclei. Therefore, we hypothesize that the changes of chromatin structure in the irradiated lymphocytes might increase the probability of a translocation during G1 and S(G2) stages of the cell cycle. The fact that the genes involved in the t(8;14) translocation are also located close together in a certain fraction of cells substantiates the hypothesis that physical distance plays an important role in the processes leading to the translocations that are responsible for oncogenic transformation of cells.

Cell Cycle↗

PubMed1998

BCR-ABL delays apoptosis upstream of procaspase-3 activation.

The p210(bcr-abl) protein was shown to inhibit apoptosis induced by DNA damaging agents. Apoptotic DNA fragmentation is delayed in the bcr-abl+ K562 and KCL-22 compared with the bcr-abl- U937 and HL-60 cell lines when treated with etoposide concentrations that induce similar DNA damage in the four cell lines. By the use of a cell-free system, we show that nuclei from untreated cells that express p210(bcr-abl) remain sensitive to apoptotic DNA fragmentation induced by triton-soluble extracts from p210(bcr-abl-) cells treated with etoposide. In the four tested cell lines, apoptotic DNA fragmentation is associated with a decreased expression of procaspase-3 (CPP32/Yama/apopain) and its cleavage into a p17 active fragment, whereas the long isoform of procaspase-2 (ICH-1L) remains unchanged and the poly(adenosine diphosphate-ribose)polymerase protein is cleaved. These events are delayed in bcr-abl+ compared with bcr-abl- cell lines. The role of p210(bcr-abl) in this delay is confirmed by comparing the effect of etoposide on the granulocyte-macrophage colony-stimulating factor (GM-CSF)-dependent UT7 cells and the bcr-abl-transfected GM-CSF-independent UT7/9 clone. We conclude that the cytosolic pathway that leads to apoptotic DNA fragmentation in etoposide-treated leukemic cells is delayed upstream of procaspase-3-mediated events in bcr-abl+ cell lines.

Apoptosis↗

PubMed1993

An actin-binding function contributes to transformation by the Bcr-Abl oncoprotein of Philadelphia chromosome-positive human leukemias.

In Philadelphia chromosome-positive human leukemias, which include chronic myelogenous leukemia and some acute lymphocytic leukemias, the c-abl proto-oncogene on chromosome 9 becomes fused to the bcr gene on chromosome 22, and Bcr-Abl fusion proteins are produced. The Bcr sequences activate the Abl tyrosine kinase which is required for the transforming function of Bcr-Abl. The Bcr sequences also enhance an F-actin-binding activity associated with c-Abl. Here, we show that binding of c-Abl and Bcr-Abl proteins to actin filaments in vivo and in vitro is mediated by an evolutionarily conserved domain at the C-terminal end of c-Abl. The c-Abl F-actin-binding domain contains a consensus motif found in several other actin-crosslinking proteins. Mutations in the consensus motif are shown to abolish binding to F-actin. Bcr-Abl proteins unable to associate with F-actin have a reduced ability to transform Rat-1 fibroblasts and to abrogate the requirement for interleukin-3 in the lymphoblastoid cell line Ba/F3. In transformed cells, Bcr-Abl induces a redistribution of F-actin into punctate, juxtanuclear aggregates. The binding to actin filaments has important implications for the pathogenic and physiological functions of the Bcr-Abl and c-Abl proteins.

Actin Cytoskeleton↗

PubMed1987

Unique fusion of bcr and c-abl genes in Philadelphia chromosome positive acute lymphoblastic leukemia.

The Philadelphia (Ph) chromosome, the product of t(9:22), is the cytogenetic hallmark of chronic myelogenous leukemia. The c-abl oncogene on chromosome 9 is translocated to the Ph chromosome and linked to a breakpoint cluster region (bcr), which is part of a large bcr gene. This results in the formation of a bcr-c-abl fusion gene, which is transcribed into an 8.5 kb chimeric mRNA encoding a 210 kd bcr-c-abl fusion protein. The Ph chromosome is also found in acute lymphoblastic leukemia (Ph+ ALL). Although the c-abl is translocated and a new 190 kd c-abl protein has been identified, no breakpoints are observed in the bcr (Ph+bcr- ALL). Here we show that in Ph+bcr- ALL, breakpoints in chromosome 22 occur within the same bcr gene, but more 5' of the bcr. Cloning of a chimeric bcr-c-abl cDNA demonstrates that the fusion gene is transcribed into a 7 kb mRNA, encoding a novel fusion protein.

Base Sequence↗

PubMedDate not supplied

Structural organization of the bcr gene and its role in the Ph' translocation.

The Philadelphia (Ph') chromosome, an abnormal chromosome 22 (ref. 1), is one of the best-known examples of a specific human chromosomal abnormality strongly associated with one form of human leukaemia, chronic myelocytic leukaemia (CML). The finding that a small region of chromosome 9 which includes the c-abl oncogene is translocated to chromosome 22 prompted studies to elucidate the molecular mechanisms involved in this disease. We have demonstrated previously that the chromosome 9 of one patient with CML contains a breakpoint 14 kilobases (kb) 5' of the most 5' v-abl-homologous exon. These data suggest a role for c-abl in CML, a theory supported by the presence of an abnormally sized abl messenger RNA and protein in the CML cell line K562. The region involved in the translocation on chromosome 22 has also been identified: all Ph'-positive patients examined to date have a breakpoint within a 5.8-kb region, for which we have proposed the name 'breakpoint cluster region' (bcr). To determine whether bcr contains protein-encoding regions, probes from bcr were tested for their ability to hybridize to complementary DNA sequences. A 0.6-kb HindIII/BamHI bcr restriction enzyme fragment proved suitable for isolating several cDNA clones from a human fibroblast cDNA library. Using bcr cDNA sequences, we obtained data strongly suggesting the presence of a chimaeric bcr/abl mRNA in the leukaemic cells of Ph'-positive CML patients. The recent isolation of cDNA clones containing bcr and abl sequences confirms this finding. Because the bcr part of the chimaeric mRNA could be required to induce the transforming activity of the human c-abl oncogene, we have now initiated studies to characterize the normal 'bcr gene' and to determine the effect of a translocation within its coding domain. We demonstrate that as a result of the Ph' translocation, a variable number of bcr exons are included in the chimaeric bcr/abl mRNA. The bcr gene sequences in this mRNA could be responsible for the transition of the abl cellular proto-oncogene into an oncogene.

Base Sequence↗

PubMed1990

Chronic myeloid leukemia with unusual variant Ph translocation (22;22)(q11;q13). Two cases with chimeric BCR-ABL transcripts.

We studied two cases of chronic myelogenous leukemia (CML) with unusual variant Philadelphia (Ph) translocation (22;22)(q11;q13). Southern blot analysis showed a chromosomal break in the BCR gene within the 5.8-kilobase (kb) breakpoint cluster region (bcr), between bcr exons 2 and 3 and between bcr exons 3 and 4, respectively. Chimeric bcr-abl mRNA was detected using polymerase chain reaction (PCR) which amplified, according to the respective bcr breakpoints, bcr exon 2-abl exon II and bcr exon 3-abl exon II junction products. These results further support the involvement, even when not cytogenetically detectable, of the 9q34 chromosomal region in all variant Ph translocations and that BCR-ABL gene fusion products are causally involved in the development of Ph positive CML.

Adult↗

PubMed1999

Detection of BCR-ABL transcripts in chronic myeloid leukemia (CML) using a 'real time' quantitative RT-PCR assay.

Quantitative competitive RT-PCR techniques have been developed to detect BCR-ABL fusion transcripts in CML but they are hardly reproducible. In this work, we have developed BCR-ABL quantification by real time RT-PCR using the ABI PRISM 7700 (Perkin Elmer), a new technique which allows simple and rapid quantification of a target sequence during the extension phase of PCR amplifications. A fluorogenic probe labeled with both a reporter dye at the 5' end and a quencher-dye at the 3' end hybridizes to the target sequence on the third exon of the ABL gene. The exonuclease activity of the Taq DNA polymerase cleaves the probe and releases the reporter dye, resulting in an increase in the fluorescence signal. The absolute copy number of the target sequence (BCR-ABL) or a control gene (ABL) in an unknown sample can then be calculated using a calibration curve prepared from a set of BCR-ABL RNA standards, and results are expressed as a BCR-ABL/ABL ratio. In our hands, the sensitivity of a serial dilution of total RNA from a positive cell line (K562) in a negative cell line (HL60) was 10(-4). Fifteen CML patients in cytogenetic CR, including 11 allografted patients, two autografted patients and two patients treated by IFN were studied sequentially by this new real time quantitative RT-PCR technique in parallel with conventional qualitative two round nested RT-PCR. The two autografted patients showed high BCR-ABL/ABL ratio in all samples. The two patients treated by IFN showed a progressive decrease in the ratio. In the 11 allografted patients, four were sequentially studied 2 years or more after allo-BMT, and all ratios were below 10(-4). The four patients remained in clinical and cytogenetic CR. The seven other allografted patients were studied immediately after the procedure. Three of them showed a progressive decrease in the BCR-ABL/ABL ratio which reached 10(-4) 7 months after allo-BMT. The three patients remained in hematologic and cytogenetic CR. The remaining four allografted patients had progressive increase of BCR-ABL ratio; three developed cytogenetic relapse 9, 11, 28 months after allo-BMT, and the last patient remained in cytogenetic CR in the bone marrow but developed granulocytic sarcoma. Results of real-time quantitative RT-PCR were in agreement with those of qualitative two round nested PCR. However, evolution changes in the results of real-time quantitative RT-PCR often preceded those of the conventional technique: a decrease of the BCR-ABL/ABL ratio preceded progression from first round to second round positivity and then negativity with the classical technique; conversely, an increase in the ratio preceded evolution with the classical technique. Thus, real-time quantitative RT-PCR may show better correlation with clinical and cytogenetic evolution than conventional qualitative techniques and may help in making early therapeutic decisions in CML, especially after molecular relapse.

Adult↗

PubMed2002

p38 MAPK-mediated activation of NF-kappaB by the RhoGEF domain of Bcr.

The oncogenic fusion protein p210 Bcr-Abl is causally associated with virtually all cases of chronic myelogenous leukemia. The wild-type Bcr product has several recognizable structural and functional motifs including a domain that contains guanine nucleotide exchange activity for Rho family GTPases (DH/PH domain). Although this domain is retained within p210 Bcr-Abl, it has no known signaling activities in vivo. Here we report that a fragment of Bcr that encodes the isolated DH/PH domain is a potent activator of the NF-kappaB transcription factor. Within the context of full length Bcr, this activity is regulated by proximal flanking sequences that suppress the DH/PH domain encoded guanine nucleotide exchange activity. NF-kappaB activation by Bcr is not mediated by nuclear translocation, but rather by p38 mitogen-activated protein kinase (MAPK)-dependent modification of the RelA/p65 transactivation domain. Although we were able to demonstrate that Bcr can function as an exchange factor for Cdc42 in vivo, NF-kappaB activation appears to occur via a Cdc42-independent mechanism. These studies constitute direct evidence that the Bcr RhoGEF domain can function in vivo, and identify a new signaling activity that may contribute to the transforming potential of p210 Bcr-Abl.

3T3 Cells↗

PubMed2003

Constitutive and specific activation of STAT3 by BCR-ABL in embryonic stem cells.

BCR-ABL oncogene, the molecular hallmark of chronic myelogenous leukemia (CML) arises in a primitive hematopoietic stem cell with both differentiation and self-renewal ability. To study the phenotypic effects of BCR-ABL in a clonal in vitro self-renewal and differentiation model, we have introduced BCR-ABL in the ES cell line CCE. The major effect of BCR-ABL expression was the persistence of primitive morphology of ES cells despite LIF deprivation, correlated with a constitutive activation of STAT3, the major self-renewal factor of ES cells, but no evidence of activation of STAT5. The enforced expression of BCR-ABL in an ES cell line, engineered to express a tetracycline-inducible dominant-negative form of a STAT3, triggered ES cell differentiation with an increased generation of hematopoietic cells expressing erythroid and megakaryocytic phenotypes. RT-PCR analysis for Oct4, Brachyury and beta-globin expression confirmed a delay of differentiation in BCR-ABL expressing clones, which could be entirely reversed upon activation of the dominant-negative form of STAT3. To study the possible relevance of STAT3 activation by BCR-ABL in human CML, Western blot analyses performed on the CD34+ cells, purified from CML patients at different stages of their disease, also demonstrated increased levels of STAT3 proteins phosphorylated both on tyrosine and serine residues. These results represent to our knowledge the first functional link between BCR-ABL oncogene and a self-renewal in the context of ES cells through constitutive activation of STAT3. Thus, the BCR-ABL embryonic stem cell model that we developed as well as the results obtained in human CML samples suggests a role for STAT3 in the pathogenesis of human CML.

Antigens, CD34↗

PubMed2005

Chronic myeloid leukaemia: an investigation into the role of Bcr-Abl-induced abnormalities in glucose transport regulation.

In chronic myeloid leukaemia (CML) expression of the chimeric tyrosine kinase, Bcr-Abl, promotes the inappropriate survival of haemopoietic stem cells by a nonautocrine mechanism in the absence of IL-3. Stimulation of glucose uptake appears to play an important role in the suppression of apoptosis by this cytokine in normal haemopoietic cells. To investigate whether the cell survival mechanisms mediated by the oncoprotein and cytokine showed any similarities, we employed a haemopoietic cell line, TonB210, engineered for inducible expression of Bcr-Abl. Tyrosine kinase expression in cytokine-deprived cells was found to mimic the effect of IL-3 in maintaining a higher V(max) for hexose uptake. In both IL-3- treated cells and those expressing Bcr-Abl, high rates of hexose uptake were associated with the retention at the cell surface of approximately 80% of the total cellular content of the GLUT1 glucose transporter. In contrast, treatment of Bcr-Abl-expressing cells for 6 h with the Bcr-Abl kinase inhibitor Glivec (10 muM), in the absence of IL-3, led to internalization of approximately 90% of the cell-surface transporters and drastically decreased (4.4+/-0.9 (mean+/-s.e.m., 4)-fold) the V(max) for hexose uptake, without significant effect on the K(m) for this process or on the total cellular transporter content. These effects were not the result of any significant loss in cell viability, and preceded the onset of apoptosis caused by inhibition of Bcr-Abl. Both IL-3 treatment and expression of Bcr-Abl led to enhanced phosphorylation of Akt (protein kinase B). The stimulation of transport by IL-3 and Bcr-Abl in TonB210 cells was inhibitable by phosphatidylinositol 3-kinase inhibitors, indicating the involvement of this kinase in the signal transduction pathway. These findings suggest that inhibition of glucose transport plays an important role in the therapeutic action of Glivec, and that the signal transduction pathways involved in transport stimulation by Bcr-Abl may offer novel therapeutic targets for CML.

Annexin A5↗

PubMed2002

The t(4;22)(q12;q11) in atypical chronic myeloid leukaemia fuses BCR to PDGFRA.

Chronic myeloid leukaemia (CML) is characterized by the presence of the BCR-ABL fusion gene, usually in association with the t(9;22)(q34;q11) translocation. We report here the identification and cloning of a rare variant translocation, t(4;22)(q12;q11), in two patients with a CML-like myeloproliferative disease (MPD). RT-PCR indicated that both patients were negative for BCR-ABL, but FISH analysis suggested that the BCR gene was rearranged. Since other translocations in MPDs frequently involve tyrosine kinases, we designed a multiplex PCR to search for mRNA fusions between BCR and three potential partner genes at 4q12: KIT, KDR and PDGFRA. An unusual inframe BCR-PDGFRA fusion mRNA was identified in both patients, with either BCR exon 7 or exon 12 fused to short BCR intron-derived sequences, which were in turn fused to part of PDGFRA exon 12. Sequencing of the genomic breakpoint junctions showed that the chromosome 22 breakpoints fell in BCR introns whereas the chromosome 4 breakpoints were within PDGFRA exon 12. This is the first report of a fusion gene that involves PDGFRA. Our findings indicate that apparently simple cytogenetic variants of t(9;22) do not always mask a cryptic BCR-ABL fusion, even when found in association with clinical and haematological indications of CML.

Adult↗