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At least 19 recordsLinked to original sources
PubMed2002

Heterogenic molecular basis for loss of ABL1-BCR transcription: deletions in der(9)t(9;22) and variants of standard t(9;22) in BCR-ABL1-positive chronic myeloid leukemia.

The objective of this study was to characterize the ABL1-BCR fusion gene in 76 BCR-ABL1-positive chronic myeloid leukemia (CML) patients regarding expression as well as genomic status, to assess the frequency of ABL1-BCR gene deletion in these patients, which has been reported to be an adverse prognostic factor in Philadelphia chromosome-positive CML. Patients were analyzed for ABL1-BCR 1b-b3 and/or 1b-b4 transcription by RT-PCR analysis. ABL1-BCR gene status was analyzed by FISH in 16 CML patients with no ABL1-BCR transcript. FISH revealed a partial or total deletion of the ABL1-BCR gene in 9/16 and localized the 5' portion of ABL1 and the 3' portion of BCR at separated loci in 5/16 patients. The latter FISH pattern resulted from a nonreciprocal translocation in two and a complex translocation in three individuals. In 2/16 patients, FISH could not exclude an intact ABL1-BCR fusion gene. Thus, most CML patients without ABL1-BCR transcript could be characterized cytogenetically to belong to two major subgroups: a silent ABL1-BCR gene was attributed to a deletion in der(9)t(9;22) in 56% of the investigated patients or to variants of a standard t(9;22) (approximately 31%). Conversely, none of the 50 patients with an ABL1-BCR transcript exhibited a variant t(9;22) in GTG-banding analysis. Thus, genomic aberrations such as deletions or complex genomic rearrangements are the basic and most frequent cause for ABL1-BCR RNA negativity in CML. The heterogeneity of the underlying molecular mechanisms may explain divergent clinical implications described for patients with an ABL1-BCR deletion and those with no ABL1-BCR transcript.

Chromosome Deletion↗
PubMed2006

BCR-ABL1 induces aberrant splicing of IKAROS and lineage infidelity in pre-B lymphoblastic leukemia cells.

Pre-B lymphoblastic leukemia cells carrying a BCR-ABL1 gene rearrangement exhibit an undifferentiated phenotype. Comparing the genome-wide gene expression profiles of normal B-cell subsets and BCR-ABL1+ pre-B lymphoblastic leukemia cells by SAGE, the leukemia cells show loss of B lymphoid identity and aberrant expression of myeloid lineage-specific molecules. Consistent with this, BCR-ABL1+ pre-B lymphoblastic leukemia cells exhibit defective expression of IKAROS, a transcription factor needed for early lymphoid lineage commitment. As shown by inducible expression of BCR-ABL1 in human and murine B-cell precursor cell lines, BCR-ABL1 induces the expression of a dominant-negative IKAROS splice variant, termed IK6. Comparing matched leukemia sample pairs from patients before and during therapy with the BCR-ABL1 kinase inhibitor STI571 (Imatinib), inhibition of BCR-ABL1 partially corrected aberrant expression of IK6 and lineage infidelity of the leukemia cells. To elucidate the contribution of IK6 to lineage infidelity in BCR-ABL1+ cell lines, IK6 expression was silenced by RNA interference. Upon inhibition of IK6, BCR-ABL1+ leukemia cells partially restored B lymphoid lineage commitment. Therefore, we propose that BCR-ABL1 induces aberrant splicing of IKAROS, which interferes with lineage identity and differentiation of pre-B lymphoblastic leukemia cells.

Alternative Splicing↗
PubMed2004

The BCR-ABL1 kinase bypasses selection for the expression of a pre-B cell receptor in pre-B acute lymphoblastic leukemia cells.

The BCR-ABL1 kinase expressed in acute lymphoblastic leukemia (ALL) drives malignant transformation of human pre-B cells. Comparing genome-wide gene expression profiles of BCR-ABL1+ pre-B ALL and normal bone marrow pre-B cells by serial analysis of gene expression, many genes involved in pre-B cell receptor signaling are silenced in the leukemia cells. Although normal pre-B cells are selected for the expression of a functional pre-B cell receptor, BCR-ABL1+ ALL cells mostly do not harbor a productively rearranged IGH allele. In these cases, we identified traces of secondary VH gene rearrangements, which may have rendered an initially productive VH region gene nonfunctional. Even BCR-ABL1+ ALL cells harboring a functional VH region gene are unresponsive to pre-B cell receptor engagement and exhibit autonomous oscillatory Ca2+ signaling activity. Conversely, leukemia subclones surviving inhibition of BCR-ABL1 by STI571 restore responsiveness to antigen receptor engagement and differentiate into immature B cells expressing immunoglobulin light chains. BCR-ABL1 kinase activity is linked to defective pre-B cell receptor signaling and the expression of a truncated isoform of the pre-B cell receptor-associated linker molecule SLP65. Also in primary leukemia cells, truncated SLP65 is expressed before but not after treatment of the patients with STI571. We conclude that inhibition of BCR-ABL1 reconstitutes selection for leukemia cells expressing a functional (pre-) B cell receptor.

Adaptor Proteins, Signal Transducing↗
PubMed2004

Short interfering RNA (siRNA) targeting the Lyn kinase induces apoptosis in primary, and drug-resistant, BCR-ABL1(+) leukemia cells.

We studied the effects of Lyn ablation on the survival of drug-resistant chronic myelogenous leukemia (CML) blast crisis cells using siRNA. Lyn siRNA reduced Lyn protein in both normal hematopoietic cells and BCR-ABL1-expressing (BCR-ABL1(+)) blasts by 80-95%. Within 48 h, siRNA-treated BCR-ABL1(+) blasts underwent apoptosis, whereas normal cells remained viable. This increased dependence on Lyn signaling for BCR-ABL1(+) blast survival provides the basis for rational treatment of drug-resistant CML blast crisis, particularly when lymphoid in nature.

Apoptosis↗
PubMed2005

Coexistence of different clonal populations harboring the b3a2 (p210) and e1a2 (p190) BCR-ABL1 fusion transcripts in chronic myelogenous leukemia resistant to imatinib.

In this study, we report the case of a Philadelphia (Ph) positive chronic myelogenous leukemia (CML) patient with the presence of p190 and p210 BCR-ABL1 mRNA fusion transcripts derived from e1a2 and b3a2 BCR-ABL1 genomic rearrangements, respectively. The presence of e1a2 BCR-ABL1 genomic rearrangement was seen in 2 different clones, one with the rearrangement and another one with the rearrangement and deletion of the BCR gene of the non-rearranged chromosome 22. After treatment with imatinib, the p210 transcript could not be detected, whereas p190 was still present 6 months after initiation of imatinib therapy and progression to blast phase. The absence of p210 transcript post treatment indicates that the clone with b3a2 responded to imatinib and that the observed resistance was associated to cells harboring the e1a2 genomic rearrangement. Despite resistance of this patient to imatinib, no evidence of mutations in the kinase domain of ABL1 was found. Loss of normal BCR in one cell clone may contribute to the resistance to imatinib due to the lack of BCR mediated inhibition of BCR-ABL1.

Aged↗
PubMed2007

FIP1L1-PDGFRA in chronic eosinophilic leukemia and BCR-ABL1 in chronic myeloid leukemia affect different leukemic cells.

We investigated genetically affected leukemic cells in FIP1L1-PDGFRA+ chronic eosinophilic leukemia (CEL) and in BCR-ABL1+ chronic myeloid leukemia (CML), two myeloproliferative disorders responsive to imatinib. Fluorescence in situ hybridization specific for BCR-ABL1 and for FIP1L1-PDGFRA was combined with cytomorphology or with lineage-restricted monoclonal antibodies and applied in CML and CEL, respectively. In CEL the amount of FIP1L1-PDGFRA+ cells among CD34+ and CD133+ cells, B and T lymphocytes, and megakaryocytes were within normal ranges. Positivity was found in eosinophils, granulo-monocytes and varying percentages of erythrocytes. In vitro assays with imatinib showed reduced survival of peripheral blood mononuclear cells but no reduction in colony-forming unit growth medium (CFU-GM) growth. In CML the BCR-ABL1 fusion gene was detected in CD34+/CD133+ cells, granulo-monocytes, eosinophils, erythrocytes, megakaryocytes and B-lymphocytes. Growth of both peripheral blood mononuclear cells and CFU-GM was inhibited by imatinib. This study provided evidence for marked differences in the leukemic masses which are targeted by imatinib in CEL or CML, as harboring FIP1L1-PDGFRA or BCR-ABL1.

AC133 Antigen↗
PubMed2006

Acute monocytic leukemia with coexpression of minor BCR-ABL1 and PICALM-MLLT10 fusion genes along with overexpression of HOXA9.

The t(9;22)(q34;q11) translocation occurs in chronic myeloid leukemia (CML) and adult B-cell acute lymphoblastic leukemia (ALL), leading to fusion of BCR to ABL1 and constitutive activation of ABL1 tyrosine kinase activity. The main BCR-ABL1 breakpoints result in P190 BCR-ABL1 or P210 BCR-ABL1 fusion proteins. The latter is found in almost all cases of CML and in one third of the cases of t(9;22)-positive adult B-ALL. P190 BCR-ABL1 is found in the remaining two thirds of t(9;22)-positive adult B-ALL cases but only exceptionally in CML. We describe here the first case of t(9;22)(q34;q11) associated with t(10;11)(p13;q14) in acute monocytic leukemia. The recurrent t(10;11)(p13;q14) translocation, usually found in acute myeloid leukemia (AML) and T-ALL, merges PICALM to MLLT10. RT-PCR enabled identification of PICALM-MLLT10 and BCR-ABL1 e1-a2 fusion transcripts; in the context of chronic and acute myeloid leukemia, the latter usually has a monocytic presentation. We also identified overexpression of HOXA9, a gene essential to myeloid differentiation that is expressed in PICALM-MLLT10 and MLL-rearranged acute leukemias. This case fits with and extends a recently proposed multistage AML model in which constitutive activation of tyrosine kinases by mutations (BCR-ABL1) are associated with deregulation of transcription factors central to myeloid differentiation (HOXA9 secondary to PICALM-MLLT10).

Adolescent↗
PubMed2000

Reversibility of acute B-cell leukaemia induced by BCR-ABL1.

Cancer is thought to arise from multiple genetic events that establish irreversible malignancy. A different mechanism might be present in certain leukaemias initiated by a chromosomal translocation. We have taken a new approach to determine if ablation of the genetic abnormality is sufficient for reversion by generating a conditional transgenic model of BCR-ABL1 (also known as BCR-ABL)-induced leukaemia. This oncogene is the result of a reciprocal translocation and is associated with different forms of leukaemia. The most common form, p210 BCR-ABL1, is found in more than 90% of patients with chronic myelogenous leukaemia (CML) and in up to 15% of adult patients with de novoacute lymphoblastic leukaemia (ALL). Efforts to establish a useful transgenic model have been hampered by embryonic lethality when the oncogene is expressed during embryogenesis, by reduced penetrance or by extremely long latency periods. One model uses the 'knock-in' approach to induce leukaemia by p190 BCR-ABL1(ref. 10). Given the limitations of models with p210, we used a different experimental approach. Lethal leukaemia developed within an acceptable time frame in all animals, and complete remission was achieved by suppression of BCR-ABL1expression, even after multiple rounds of induction and reversion. Our results demonstrate that BCR-ABL1is required for both induction and maintenance of leukaemia.

Adult↗
PubMed2026

Dual functional genomics reveals a broad and convergent landscape of asciminib resistance in BCR::ABL1.

BACKGROUND: Drug resistance is a constantly evolving challenge. The allosteric inhibitor asciminib is a novel therapy for chronic myelogenous leukemia (CML) that targets the myristoyl pocket of the BCR::ABL1 kinase. While it can overcome resistance to active-site inhibitors like imatinib, new resistance mutations to asciminib are emerging. The complete landscape of these mutations, particularly those outside the kinase domain or those arising from epistatic interactions between mutations, are not well understood. METHODS: This study employed a dual functional genomics approach in CML cell line models. A high-throughput adenosine base editing (ABE) screen was used to identify broad hotspots of asciminib resistance across the entire BCR::ABL1 protein. Deep mutational scanning (DMS) was then used to create a high-resolution map of all possible amino acid changes within these hotspots. An "edit-on-edit" screen was performed to investigate epistasis by introducing a library of mutations into a cell line that was pre-edited to incorporate the common imatinib-resistance mutation, Y253H. Finally, a novel Förster resonance energy transfer (FRET) biosensor was developed to measure the conformational state of BCR::ABL1 in live cells and link it to drug sensitivity. RESULTS: The screens identified 279 asciminib resistance mutations and revealed resistance hotspots distributed across the SH3, SH2, and kinase domains, in contrast to imatinib resistance, which is largely confined to the kinase domain. The study uncovered a potent epistatic interaction between a mutation in the SH3 domain (V73A) and a mutation in the kinase domain P-loop (Y253H), which synergistically conferred high-level resistance. The FRET biosensor demonstrated that asciminib resistance mutations tend to destabilize the "closed" inactive conformation of the ABL1 kinase. CONCLUSIONS: The landscape of asciminib resistance is broader and more complex than previously appreciated, involving mutations across multiple domains that disrupt ABL1 autoinhibition. Epistasis between mutations acquired during sequential therapies can create unexpected and potent resistance. However, these diverse genetic resistance mechanisms converge on a single biophysical measurement of the openness of the active ABL1 conformation. This provides a unified framework for understanding asciminib resistance and underscores the need for routine clinical resistance monitoring to include the SH3 and SH2 domains in first line and later line therapy.

Fusion Proteins, bcr-abl↗
PubMed2026

Late acquisition of BCR::ABL1 during clonal evolution of SAMD9-associated MDS with phenotypic shift from AML to B-ALL.

We describe a unique case of SAMD9-associated myelodysplastic syndrome (MDS) with monosomy 7 that evolved over 16 years into BCR::ABL1-positive acute myeloid leukemia (AML) and subsequently manifested as B-cell acute lymphoblastic leukemia (B-ALL). Genomic analysis at AML diagnosis revealed a germline SAMD9 mutation together with somatic RUNX1 and PPM1D mutations, supporting stepwise clonal evolution, with BCR::ABL1 emerging as a late leukemogenic event. The dominant leukemic population at AML onset showed myeloid morphology and immunophenotype, whereas a minor CD19+CD10+ population was already detectable. Following venetoclax and azacitidine therapy, the dominant leukemic phenotype shifted to B-ALL while retaining BCR::ABL1 positivity. Detection of the Philadelphia chromosome in mature neutrophils at both AML onset and ALL relapse supported multilineage involvement of a multipotent BCR::ABL1-positive clone. Ponatinib achieved disease control. This case highlights late acquisition of BCR::ABL1 during SAMD9-associated clonal evolution and therapy-driven phenotypic shift within a shared Ph-positive leukemic stem-cell hierarchy.

Humans↗
PubMed2002

Identical abnormality of the short arm of chromosome 18 in two Philadelphia-positive chronic myelocytic leukemia patients with erythroblastic transformation, resulting in duplication of BCR-ABL1 fusion.

Two patients with Ph-positive chronic myelocytic leukemia in erythroblastic transformation and rearrangement of the short arm of chromosome 18 are reported. Fluorescence in situ hybridization studies showed that the 18p rearrangement resulted from translocation of the main part of chromosome 22 long arm to 18p, including BCR-ABL1 fusion. The 18p abnormality resulted, thus, in loss of 18p and duplication of BCR-ABL1 in both patients. The possible relation to the erythroblastic type of blastic phase is briefly discussed. In addition an apparently intact germline ABL1 gene was duplicated and inserted into chromosome 6 at band p21 in one of these patients.

Aged↗
PubMed2004

Interference of BCR-ABL1 kinase activity with antigen receptor signaling in B cell precursor leukemia cells.

The chromosomal translocation t,(9;22) resulting in the fusion of the BCR and ABL1 genes, represents a recurrent aberration in B cell precursor leukemia cells. Their normal counterparts, B cell precursor cells, are positively selected for survival signals through the antigen receptor, whose expression requires a functional immunoglobulin heavy chain (IGH) gene rearrangement. Unexpectedly, B cell precursor leukemia cells harboring a BCR-ABL1 gene rearrangement do not depend on antigen receptor mediated survival signals. Genes involved in the signaling cascade of the antigen receptor are silenced and in most cases, the dominant tumor clone does not carry a functional IGH gene rearrangement. However, upon inhibition of the BCR-ABL1 kinase activity by STI571, only leukemia cells expressing an antigen receptor are able to survive. Since resistance to STI571 is frequent in the therapy of BCR-ABL1(+) B cell precursor leukemia, antigen receptor signaling may represent a mechanism through which these cells can temporarily evade STI571-induced apoptosis. This may open a time frame, during which leukemia cells acquire secondary transforming events that confer definitive resistance to STI571.

Animals↗
PubMed2004

Requirement of Src kinases Lyn, Hck and Fgr for BCR-ABL1-induced B-lymphoblastic leukemia but not chronic myeloid leukemia.

The Abl kinase inhibitor imatinib mesylate is the preferred treatment for Philadelphia chromosome-positive (Ph(+)) chronic myeloid leukemia (CML) in chronic phase but is much less effective in CML blast crisis or Ph(+) B-cell acute lymphoblastic leukemia (B-ALL). Here, we show that Bcr-Abl activated the Src kinases Lyn, Hck and Fgr in B-lymphoid cells. BCR-ABL1 retrovirus-transduced marrow from mice lacking all three Src kinases efficiently induced CML but not B-ALL in recipients. The kinase inhibitor CGP76030 impaired the proliferation of B-lymphoid cells expressing Bcr-Abl in vitro and prolonged survival of mice with B-ALL but not CML. The combination of CGP76030 and imatinib was superior to imatinib alone in this regard. The biochemical target of CGP76030 in leukemia cells was Src kinases, not Bcr-Abl. These results implicate Src family kinases as therapeutic targets in Ph(+) B-ALL and suggest that simultaneous inhibition of Src and Bcr-Abl kinases may benefit individuals with Ph(+) acute leukemia.

Animals↗
PubMed2026

Genetic Profile, Treatment Response, and Outcomes of BCR::ABL1-Positive Mixed-Phenotype Acute Leukemia: A Study From the BCR::ABL1 Pathology Group.

Mixed-phenotype acute leukemia (MPAL) with BCR::ABL1 fusion is rare, and its clinicopathological features, genetic landscape, therapeutic response, and patient outcomes remain incompletely defined, as does its relationship to blast-phase chronic myeloid leukemia. In this multicenter study of 44 patients, 86.4% had B/myeloid MPAL, 72.7% showed lymphoid predominance, 40.9% had complex karyotypes, and 68.3% harbored somatic mutations, most commonly RUNX1 mutations (46.3%). RUNX1 mutations frequently co-occurred with acute myeloid leukemia (AML)-associated alterations, whereas DNMT3A, TET2, and BCORL1 mutations were restricted to RUNX1-mutated cases. In contrast, acute lymphoblastic leukemia (ALL)-associated alterations (IKZF1 mutation/deletion and ETV6 mutations) were confined to RUNX1-wild-type patients. TP53 and signaling pathway mutations (NRAS, KRAS, PTPN11, and FLT3) were not detected. Forty-two patients received induction chemotherapy and/or immunotherapy combined with tyrosine kinase inhibitors: 74.2% of lymphoid-predominant patients and 63.6% of myeloid-predominant patients received ALL- and AML-type therapies, respectively. Ten patients relapsed, and 2 had primary refractory disease; some exhibited a dynamic shift in predominant lineage immunophenotype, chromosomal alterations, and somatic mutations at the relapse or refractory stage. The overall remission rate was 86.8%, with no significant differences across ALL-, AML-, or hybrid-type regimens. After a median follow-up of 24.2 months, the median overall survival was 52.5 months. Complex karyotype was associated with inferior overall survival compared with cases lacking additional chromosomal alterations (P = .02), whereas RUNX1 mutations were not. No significant differences in genetic profiles, treatment response, or outcomes were observed between patients with and without chronic myeloid leukemia-like features. This study provides a comprehensive genomic and clinical characterization of BCR::ABL1-positive MPAL, supporting improved risk stratification and future therapeutic strategies.

Adolescent↗
PubMed2001

Nonrandom distribution of interspersed repeat elements in the BCR and ABL1 genes and its relation to breakpoint cluster regions.

The Philadelphia translocation, t(9;22)(q34;q11), is the microscopically visible product of recombination between two genes, ABL1 on chromosome 9 and BCR on chromosome 22, and gives rise to a functional hybrid BCR-ABL1 gene with demonstrated leukemogenic properties. Breakpoints in BCR occur mostly within one of two regions: a 5 kb major breakpoint cluster region (M-Bcr) and a larger 35 kb minor breakpoint cluster region (m-Bcr) towards the 3' end of the first BCR intron. By contrast, breakpoints in ABL1 are reported to occur more widely across a >200 kb region which spans the large first and second introns. The mechanisms that determine preferential breakage sites in BCR, and which cause recombination between BCR and ABL1, are presently unknown. In some cases, Alu repeats have been identified at or near sequenced breakpoint sites in both genes, providing indications, albeit controversial, that they may be relevant. For the present study, we carried out a detailed analysis of genomic BCR and ABL1 sequences to identify, classify, and locate interspersed repeat sequences and to relate their distribution to precisely mapped BCR-ABL1 recombination sites. Our findings confirm that Alu are the most abundant class of repeat in both genes, but that they occupy fewer sites than previously estimated and that they are distributed nonrandomly. r-Scan statistics were applied to provide a measure of repeat distribution and to evaluate extremes in repeat spacing. A significant lack of Alu elements was observed across the major and minor breakpoint cluster regions of BCR and across a 25-kb region showing a high frequency of breakage in ABL1. These findings counter the suggestion that occurrence of Alu at BCR-ABL1 recombination sites is likely by chance because of the high density of Alu in these two genes. Instead, as yet unidentified DNA conformation or nucleotide characteristics peculiar to the preferentially recombining regions, including those Alu elements present within them, more likely influence their fragility.

Alu Elements↗
PubMed2005

Distinct patterns of hematopoietic stem cell involvement in acute lymphoblastic leukemia.

The cellular targets of primary mutations and malignant transformation remain elusive in most cancers. Here, we show that clinically and genetically different subtypes of acute lymphoblastic leukemia (ALL) originate and transform at distinct stages of hematopoietic development. Primary ETV6-RUNX1 (also known as TEL-AML1) fusions and subsequent leukemic transformations were targeted to committed B-cell progenitors. Major breakpoint BCR-ABL1 fusions (encoding P210 BCR-ABL1) originated in hematopoietic stem cells (HSCs), whereas minor BCR-ABL1 fusions (encoding P190 BCR-ABL1) had a B-cell progenitor origin, suggesting that P190 and P210 BCR-ABL1 ALLs represent largely distinct tumor biological and clinical entities. The transformed leukemia-initiating stem cells in both P190 and P210 BCR-ABL1 ALLs had, as in ETV6-RUNX1 ALLs, a committed B progenitor phenotype. In all patients, normal and leukemic repopulating stem cells could successfully be separated prospectively, and notably, the size of the normal HSC compartment in ETV6-RUNX1 and P190 BCR-ABL1 ALLs was found to be unaffected by the expansive leukemic stem cell population.

ADP-ribosyl Cyclase↗
PubMed2005

Mimicry of a constitutively active pre-B cell receptor in acute lymphoblastic leukemia cells.

Pre-B cells undergo apoptosis unless they are rescued by pre-B cell receptor-dependent survival signals. We previously showed that the BCR-ABL1 kinase that is expressed in pre-B lymphoblastic leukemia bypasses selection for pre-B cell receptor-dependent survival signals. Investigating possible interference of BCR-ABL1 with pre-B cell receptor signaling, we found that neither SYK nor SLP65 can be phosphorylated in response to pre-B cell receptor engagement. Instead, Bruton's tyrosine kinase (BTK) is constitutively phosphorylated by BCR-ABL1. Activated BTK is essential for survival signals that otherwise would arise from the pre-B cell receptor, including activation of PLCgamma1, autonomous Ca2+ signaling, STAT5-phosphorylation, and up-regulation of BCLX(L). Inhibition of BTK activity specifically induces apoptosis in BCR-ABL1+ leukemia cells to a similar extent as inhibition of BCR-ABL1 kinase activity itself. However, BCR-ABL1 cannot directly bind to full-length BTK. Instead, BCR-ABL1 induces the expression of a truncated splice variant of BTK that acts as a linker between the two kinases. As opposed to full-length BTK, truncated BTK lacks kinase activity yet can bind to BCR-ABL1 through its SRC-homology domain 3. Acting as a linker, truncated BTK enables BCR-ABL1-dependent activation of full-length BTK, which initiates downstream survival signals and mimics a constitutively active pre-B cell receptor.

Adolescent↗