Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “BCR”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 recordsLinked to original sources
PubMed1992

Minor BCR (m-bcr) rearrangements may appear in major BCR (M-bcr)-positive CML cases.

The chromosome 22 derivative, the Philadelphia (Ph) chromosome, results from the reciprocal translocation t(9;22) (q34;q11). On DNA level a BCR/ABL rearrangement involving the so-called major BCR (Mbcr) from chromosome 22 has been associated with chronic myeloid leukemia (CML). For Ph+ ALL a site of rearrangements in the 5' part of the BCR (breakpoint cluster region) gene on chromosome 22, the so-called minor bcr region (mbcr) has been described within the first intron in a 10.8 kb region (=bcr2 or m-BCR1). The BB1 probe detects two Eco fragments of 8.5 and/or 11 kb, which may appear as monomorphic or heteromorphic alleles, both covering bcr2. We have analyzed EcoRI restriction polymorphisms within bcr2 in 42 patients with a rearrangement in M-bcr (including 39 Philadelphia chromosome-positive (Ph+) CML patients and 3 ALLs) and in 18 healthy unrelated volunteers. Of the 42 patients tested, 52.4% (22) had the 8.5 kb bcr2 allele, 21.4% (9) had the 11 kb bcr2 allele, and 26.2% (11) had both the 8.5 and the 11 kb allele. In addition to normal allelic polymorphisms in bcr2, rRFs (rearranged bcr2 restriction fragments) were found in bcr2 as shown in 33% (14 of 42) of our patients. By contrast, no rRFs were found in 18 healthy volunteers. Our results indicate, that heterogeneous rearrangements in bcr2 may appear in addition to BCR/ABL rearrangements involving M-bcr in Ph+CML.

Alleles↗
PubMed1993

BCR-ABL tyrosine kinase is autophosphorylated or transphosphorylates P160 BCR on tyrosine predominantly within the first BCR exon.

The role of BCR gene sequences in Philadelphia (Ph) chromosome-positive leukemia is not well understood. Our previous studies demonstrated that P210 BCR-ABL co-precipitates with P160 BCR following immunoprecipitation with antibodies to the C-terminal domain of P160 BCR, sequences lacking in P210 BCR-ABL. We now report that tryptic peptides shared by both P160 BCR and P210 BCR-ABL are phosphorylated on tyrosine in vitro either when using immune complexes containing P160 BCR complexed to BCR-ABL or when P160 BCR is phosphorylated in trans by P210 BCR-ABL immune complexes from cells lacking functional P160 BCR. P185 BCR-ABL produced in a cell line derived from a Ph chromosome-positive acute lymphocytic leukemia patient also co-immunoprecipitated with P160 BCR. As with P210 BCR-ABL, P160 BCR tyrosine phosphopeptides were shared with P185 BCR-ABL, indicating that the major sites of tyrosine phosphorylation in vitro are contained within the first exon of P160 BCR. Similarly, BCR-ABL autophosphorylation was found to occur predominantly at tyrosines within BCR exon 1 sequences. These results raise the possibility that the activated ABL protein kinase of BCR-ABL proteins modulates the putative signal transduction activities of P160 BCR by tyrosine phosphorylation of exon 1 sequences.

Animals↗
PubMed1995

BCR-ABL, ABL-BCR, BCR, and ABL genes are all expressed in individual granulocyte-macrophage colony-forming unit colonies derived from blood of patients with chronic myeloid leukemia.

It has been suggested that the BCR-ABL gene of chronic myeloid leukemia (CML) is not uniformly expressed in Philadelphia (Ph)-positive cells, and that BCR-ABL gene expression precludes transcription of the normal BCR or ABL genes. Therefore, we have analyzed granulocyte-macrophage colony-forming unit (CFU-GM) colonies derived from peripheral blood of 11 CML patients by cytogenetic and by reverse transcriptase-polymerase chain reaction (PCR) amplification of BCR-ABL, ABL-BCR, BCR, and ABL. All CFU-GM colonies with analyzable metaphases were found to contain a Ph chromosome. In 2 patients, the initial PCR screening failed to detect BCR-ABL transcripts in 2 of 11 and 1 of 7 Ph-positive colonies. However, when amplification for BCR-ABL was repeated in quintuplicate, all but 1 colony from a single patient showed one or more positive results. Amplifications of the four genes in each colony showed that BCR-ABL, ABL-BCR, and the normal BCR and ABL were simultaneously expressed in the majority of CFU-GM colonies. Replicate PCR tests for BCR and for ABL in colonies initially scored as negative also uncovered previously undetected positive amplifications. We conclude that BCR-ABL expression does not suppress transcription from the normal BCR and ABL genes, and that Ph-positive, BCR-ABL-negative colonies derived from peripheral blood CFU-GM are rare or nonexistent.

Base Sequence↗
PubMed2000

Molecular analysis of lineage-specific chimerism and minimal residual disease by RT-PCR of p210(BCR-ABL) and p190(BCR-ABL) after allogeneic bone marrow transplantation for chronic myeloid leukemia: increasing mixed myeloid chimerism and p190(BCR-ABL) detection precede cytogenetic relapse.

We studied lineage-specific chimerism and minimal residual disease (MRD) in sequential posttransplant samples from 55 patients who underwent unmanipulated (n = 44) or partially T-cell-depleted (n = 11) allogeneic bone marrow transplantation (BMT) for chronic myeloid leukemia (CML). Chimerism was assessed by polymerase chain reaction (VNTR [variable number of tandem repeats]-PCR) analysis in highly purified CD19+, CD3+, CD15+, and CD56+ cell fractions, whereas MRD was investigated in whole blood by reverse transcriptase-PCR (RT-PCR) of both p210(BCR-ABL) and p190(BCR-ABL) hybrid transcripts. Of 55 patients, 14 (including 6 T-cell-depleted patients) had cytogenetic relapse at 5-80 months and progressed to hematologic relapse, while 41 patients remained in prolonged cytogenetic remission 12-107 months post-BMT. Before leukemia recurrence, patients in the relapse group showed a consistent evolution pattern sequentially featured by persistent p210(BCR-ABL) positivity, increasing mixed chimerism (MC) in myeloid cells, p190(BCR-ABL) positivity, and, finally, cytogenetic relapse. Myeloid MC preceded cytogenetic relapse by 2-12 months, whereas p190(BCR/ABL) was detected 1-6 months prior to cytogenetic relapse in 11 patients and concomitant with cytogenetic relapse in 3 patients. In the remission group, all patients invariably tested negative for p190(BCR-ABL); 10 patients tested positive for p210(BCR-ABL) at variable time-points but showed persistent full donor chimerism (DC), whereas 31 patients tested p210(BCR-ABL) negative and displayed full DC or transient MC due to the persistence of recipient T cells. Two patients in the relapse group were successfully reinduced into molecular remission with donor lymphocyte infusion. Sequential molecular analysis after such treatment showed the inverse pattern to that observed prior to relapse, ie, progressive disappearance of p190(BCR-ABL) transcripts, conversion of myeloid chimerism to donor type, and, finally, p210(BCR-ABL) negativity. We conclude that lineage-specific chimerism and p190(BCR-ABL) messenger RNA (mRNA) analyses contribute a better characterization of CML evolution after BMT and enable early identification of patients at the highest risk of relapse. (Blood. 2000;95:2659-2665)

Adolescent↗
PubMed2005

Disease status in patients with chronic myeloid leukemia is better characterized by BCR-ABL/BCR transcript ratio than by BCR-ABL transcript level, which may suggest a role of normal BCR gene in the disease pathogenesis.

Monitoring of BCR-ABL transcript level is widely used in chronic myeloid leukemia (CML) to follow up response to therapy. In this study we compare abilities of two quantitative RT-PCR assays to characterize the disease status in CML patients: RT-PCR quantifying the BCR-ABL transcript concentration and RT-PCR determining the BCR-ABL/BCR transcript ratio (R). We demonstrate that in non-responders only R, but not BCR-ABL, unambiguously characterizes the state of disease. Moreover, R values >1 found in all poor responders indicate lower BCR expression compared to BCR- ABL in these patients. Our results demonstrate the importance of BCR-ABL/BCR transcript ratio for the disease status and the disease prognosis characterization and suggest a possible role of the normal BCR gene expression in CML pathogenesis.

Adult↗
PubMed1999

Bcr: a negative regulator of the Bcr-Abl oncoprotein.

Chronic myelogenous leukemia is typically characterized by the presence of the Philadelphia chromosome (Ph) in which 5' portions of the BCR gene are fused to a large portion of the ABL gene. Our studies and those of others indicate that Bcr sequences within the Bcr-Abl oncoprotein are critically involved in activating the Abl tyrosine kinase and actively participate in the oncogenic response, which is generated by the Bcr-Abl oncoprotein. We investigated the role of the Bcr protein in the oncogenic effects of Bcr-Abl. Reduction of the level of the Bcr protein by incubating cells with a 3' BCR anti-sense oligodeoxynucleotide increased the growth rate and survival of hematopoietic cell lines expressing Bcr-Abl. Also, enforced expression of Bcr in Bcr-Abl cell lines strongly reduced transformation efficiency. Induction of Bcr expression drastically reduced the phosphotyrosine content of Bcr-Abl in Rat-1 fibroblasts transformed by P185 BCR-ABL and in hematopoietic cells expressing P210 Bcr-Abl within days following induction of Bcr. Rat-1/P185 cells maintained for three weeks after Bcr induction had dramatically reduced amounts of phosphotyrosine proteins compared to cells in which Bcr expression was repressed by the addition of Tet. In contrast Bcr expression did not decrease the phosphotyrosine content of either v-Src or activated Neu tyrosine kinase. Importantly, the phosphotyrosine content of total P160 BCR (induced plus endogenous) was strongly reduced by inducing expression of Bcr, indicating that the induced Bcr protein was not a target of the tyrosine kinase activity of Bcr-Abl but instead functioned as an inhibitor of Bcr-Abl. These results show that the Bcr protein can function as a negative regulator of Bcr-Abl, but that the inhibitory effects of Bcr are dependent on achieving an elevated level of Bcr expression relative to Bcr-Abl.

Animals↗
PubMed2001

BCR gene expression blocks Bcr-Abl induced pathogenicity in a mouse model.

It is well accepted that the Bcr-Abl oncoprotein encoded by the Philadelphia chromosome is responsible for causing chronic myelogenous leukemia (CML). We have previously demonstrated that expression of Bcr interferes with the oncogenic effects of Bcr-Abl. To examine the effects of increased Bcr expression on Bcr-Abl oncogenic effects in a more physiological system, we tested the leukemogenic potential of a clone of K562 cells (K6 K562) containing an inducible BCR gene in NOD/scid mice. In this clone, the BCR gene was placed under the control of a tetracycline (Tet) repression system with a cytomegalovirus (CMV) promoter. Induction of exogenous Bcr protein by removal of Tet from the culture medium caused a dramatic increase in Bcr serine kinase activity, yielding predominantly phosphoserine Bcr, despite the presence of Bcr-Abl in the kinase reaction mixture. Prior to induction, the endogenous Bcr was predominantly in the phosphotyrosine form because of phosphorylation by Bcr-Abl, which we previously have shown suppresses Bcr serine/threonine kinase activity. Injection of K6 K562 cells into NOD/scid mice under conditions where BCR expression was suppressed resulted in death or terminal illness in 100% of the mice within 35 days after injection. These mice had a severe wasting syndrome characterized by atrophy of bone marrow hematopoiesis, and/or neoplasia of liver, bone marrow and spleen. Neoplastic spleens from these mice usually contained b3a2 Bcr-Abl transcripts. In contrast, induction of BCR expression at the time of injection allowed 80% survival; these healthy mice had no detectable microscopic lesions in blood forming organs. This difference in survival was significant with P<0.0001. Of interest, mice that were fed Tet for 19 days to initiate the disease syndrome and then released from the BCR transcriptional block had a significantly better survival pattern than mice exposed to Tet throughout the entire period. Moreover, 30% of these mice (three mice) survived through day 50. We conclude from these findings that BCR gene expression strongly inhibits the oncogenic effects of Bcr-Abl in NOD/scid mice, yielding healthy mice in most cases.

Animals↗
PubMed1996

Sequences within the first exon of BCR inhibit the activated tyrosine kinases of c-Abl and the Bcr-Abl oncoprotein.

The Bcr-Abl oncoprotein is the primary causative factor in Philadelphia chromosome-associated leukemias. The activated tyrosine kinase of the Bcr-Abl oncoprotein is the primary driving force behind its oncogenic activity. We report here that a deleted form of Bcr [Bcr(64-413)], encompassing the Abl SH2 binding domains of Bcr, reduced the phosphotyrosine content of c-Abl and Bcr-Abl within cells and inhibited Bcr-Abl autophosphorylation activity in vitro. Similarly, a Bcr peptide phosphorylated on Ser-354 blocked the c-Abl and Bcr-Abl kinases in vitro, whereas the same peptide phosphorylated on Tyr-360 was not inhibitory. Bcr(64-413) was also resistant to tyrosine phosphorylation by either activated c-Abl or Bcr-Abl. Importantly, Bcr(64-413) interfered with the growth of Bcr-Abl-expressing cell lines. Our findings indicate that the Abl SH2 binding domain of Bcr in the phosphoserine form inhibits the Bcr-Abl oncoprotein but that tyrosine phosphorylation of this domain of Bcr reverses its inhibitory effects on Bcr-Abl. These results raise interesting questions about a possible role of Bcr or a Bcr-related molecule in modulating the activity of the Bcr-Abl oncoprotein and c-Abl itself.

Animals↗
PubMed2000

Frequent polymorphism in BCR exon b2 identified in BCR-ABL positive and negative individuals using fluorescent hybridization probes.

Recently, a polymorphic base in exon 13 of the BCR gene (exon b2 of the major breakpoint cluster region) has been identified in the eighth position before the junctional region of BCR-ABL cDNA. Cytosine replaces thymidine; the corresponding triplets are AAT (T allele) and AAC (C allele), respectively, both coding for asparagine. Therefore, this polymorphism has no implication in the primary structure of BCR and BCR-ABL proteins. However, since the alteration is located close to the fusion region it may have a significant influence on the annealing of PCR primers, probes for real time PCR, and antisense oligonucleotides. We have developed a RT-PCR-based screening method to easily identify polymorphic BCR and BCR-ABL alleles in CML patients and normal individuals in order to estimate their frequency. After amplification from cDNA, a melting curve of a specific fluorogenic probe mapping to the 3' end of BCR exon b2 and spanning the polymorphism readily discriminates between normal and polymorphic BCR and BCR-ABL alleles. This reporter probe is 3' labeled with fluorescein and placed next to 5' LC Red640-labeled anchor probes mapping to the 5' ends of BCR exon b3 or ABL exon a2 so that resonance energy transfer occurs when the probes are hybridized (LightCycler technology). T and C alleles were discriminated by a melting temperature difference of the reporter probe of 3.2 K. We have investigated cDNAs derived from leukocytes from seven cell lines and a total of 229 individuals: normal donors, n = 15; BCR-ABL negative chronic myeloproliferative disorders, n=30; BCR-ABL negative acute leukemias, n= 11; b2a2BCR-ABL positive CML, n = 93; and b3a2BCR-ABL positive CML, n= 80. The frequency of the C allele was 33.0% in BCR-ABL negative individuals, 30.6% in b2a2BCR-ABL, and 23.8% in b3a2BCR-ABL positive CML. In CML patients, 27.7% of BCR-ABL and 27.2% of BCR alleles had the C allele (NS). In total, 132 of 458 (28.8%) exons b2 of BCR or BCR-ABL alleles demonstrated this polymorphism. We conclude that a thymidine/cytosine replacement occurs frequently in BCR exon b2. Probes for real time quantitative RT-PCR should be designed not to map to the critical region in order to avoid underestimation of the number of BCR-ABL transcripts.

Acute Disease↗
PubMed1999

ABL-BCR expression in BCR-ABL-positive human leukemia cell lines.

Expression of normal ABL and BCR and of reciprocal fusion genes BCR-ABL and ABL-BCR was examined in a panel of 53 BCR-ABL-positive cell lines by RT-PCR to determine the influence of the various transcripts on leukemogenesis. Seventeen out of 18 lymphoid cell lines expressed ABL1a and/or ABL1b, whereas only 16 out of 35 myeloid cell lines expressed one or both normal ABL transcripts. Normal BCR was expressed in seven lymphoid cell lines; all cell lines from the m-bcr group (n = 9) were BCR-negative. Among the myeloid cell lines, 77% expressed the BCR gene. The M-bcr and m-bcr translocations were equally distributed among cell lines with lymphoid phenotype. The m-bcr translocation was not found in myeloid cell lines. b3-a2 constitutes the predominant form of fusion gene in myeloid cell lines with an incidence of about 68%. One myeloid cell line exhibited the mu-bcr variant. An ABL-BCR transcript of the 1a splice variant was not detected in any of the cell lines. ABL1b-BCR was expressed in all varieties of cell types and translocation forms: 56 and 66% in the lymphoid and myeloid cell lines, respectively; similar distributions were found for the fusion gene types: 67% among e1-a2, 73% among b2-a2, and 61% among b3-a2 translocations. Except for the lack of expression of normal BCR in m-bcr cell lines and of ABL1a-BCR expression in all cell lines, no consistent correlation of expression or lack of expression of BCR and ABL or of ABL-BCR reciprocal fusion genes could be found with cell lineages and translocation types. Further work is required to determine the exact role of the reciprocal fusion gene transcripts on the pathophysiological mechanisms of leukemogenesis.

Base Sequence↗
PubMed1997

Effect of Bcr sequences on the cellular function of the Bcr-Abl oncoprotein.

In Philadelphia chromosome (Ph1)-positive human leukemia, the c-Abl tyrosine kinase is activated by fusion to sequences encoded by the breakpoint cluster region (bcr) gene. Two major types of Bcr-Abl fusion proteins have been found in human leukemia. Fusion of the N-terminal 426 amino acids of Bcr generates p190(Bcr-Abl) which is mostly found in acute lymphocytic leukemia (ALL), whereas fusion of the N-terminal 902 or 927 amino acids of Bcr generates p210(Bcr-Abl) mostly found with chronic myelogenous leukemia (CML). Previous studies have demonstrated that both the Bcr and the Abl functional domains contribute to the oncogenic activity of Bcr-Abl proteins. Present in both p190 and p210 is the N-terminal coiled-coil of Bcr (aa 1-63), which is shown here to be functionally replaceable with the leucine zipper of the yeast transcription factor GCN4. The ZIP-Bcr-Abl protein transforms Rat-1/myc cells, is autophosphorylated on tyrosine and localized predominantly to actin filaments. Thus, formation of homo-oligomers through either Bcr or GCN4 coiled-coil can activate the tyrosine kinase and F-actin binding functions of Abl. We also found that a Bcr-Abl fusion containing only Bcr amino acids (1-191) can efficiently transform Rat-1/myc cells. Fusion of additional Bcr sequences (aa 192-923) did not affect the transformation of Rat-1/myc cells but progressively reduced the disruptive effect on the actin cytoskeleton. In particular, the Dbl homology domain present in p210(Bcr-Abl) but not in p190(Bcr-Abl) contributes to the stabilization of actin fibers. The modulatory effect of Bcr sequences on actin structure may underlie the apparent pathogenic variations between the different Bcr-Abl fusion proteins.

Actins↗
PubMed1987

Expression of bcr and bcr-abl fusion transcripts in normal and leukemic cells.

The translocation of the c-abl oncogene from chromosome 9 to the bcr gene on chromosome 22 in cases of Philadelphia chromosome-positive chronic myelogenous leukemia (CML) generates an aberrant bcr-abl fusion transcript which may be intimately related to the pathogenesis of CML. Because factors controlling normal bcr expression might also be involved in the expression of this aberrant bcr-abl transcript, we studied the patterns of expression of the normal bcr gene in different cell types. We found that the normal bcr gene was expressed in many different types of human cells. Moreover, the bcr gene was evolutionarily conserved, and homologous bcr genomic sequences and RNA transcripts were readily detected in chick tissue. The highest level of bcr expression in chick tissue was in brain tissue, the lowest level was in liver tissue, and a truncated bcr mRNA was noted in chick testes. Normal bcr transcripts, in addition to the aberrant bcr-abl hybrid transcripts, have been found in all Philadelphia chromosome-positive CML cells studied to date. Within a given CML sample, the relative amounts of normal bcr RNA and aberrant bcr-abl RNA were similar. In addition, the normal bcr and the aberrant bcr-abl hybrid transcripts demonstrated similarly prolonged half-lives compared with that of the normal abl-related transcripts in CML cells. These findings suggest that in CML cells, similar cellular mechanisms control the steady-state levels of both the normal bcr and the bcr-abl fusion RNAs.

Cell Line↗
PubMed1999

Polarized distribution of Bcr-Abl in migrating myeloid cells and co-localization of Bcr-Abl and its target proteins.

Bcr-Abl plays a critical role in the pathogenesis of Philadelphia chromosome-positive leukemia. Although a large number of substrates and interacting proteins of Bcr-Abl have been identified, it remains unclear whether Bcr-Abl assembles multi-protein complexes and if it does where these complexes are within cells. We have investigated the localization of Bcr-Abl in 32D myeloid cells attached to the extracellular matrix. We have found that Bcr-Abl displays a polarized distribution, colocalizing with a subset of filamentous actin at trailing portions of migrating 32D cells, and localizes on the cortical F-actin and on vesicle-like structures in resting 32D cells. Deletion of the actin binding domain of Bcr-Abl (Bcr-AbI-AD) dramatically enhances the localization of Bcr-Abl on the vesicle-like structures. These distinct localization patterns of Bcr-Abl and Bcr-Abl-AD enabled us to examine the localization of Bcr-Abl substrate and interacting proteins in relation to Bcr-Abl. We found that a subset of biochemically defined target proteins of Bcr-Abl redistributed and co-localized with Bcr-Abl on F-actin and on vesicle-like structures. The co-localization of signaling proteins with Bcr-Abl at its sites of localization supports the idea that Bcr-Abl forms a multi-protein signaling complex, while the polarized distribution and vesicle-like localization of Bcr-Abl may play a role in leukemogenesis.

3T3 Cells↗
PubMed2002

Inhibition of the Bcr-Abl oncoprotein by Bcr requires phosphoserine 354.

The BCR protein is involved in the inhibition of oncogenic activity of the Bcr-Abl oncoprotein. This inhibition is believed to be the result of binding to the SH2 domain of Bcr-Abl in a non-phosphotyrosine-dependent manner. We showed that the Arg to Leu mutation in the Phe-Leu-Val-Arg-Glu-Ser (FLVRES) sequence of the SH2 domain, known to interfere with phosphotyrosine sequence binding, did not block the binding of Bcr first exon sequences to the Abl SH2 domain. We examined the structural-functional properties of a first exon mutant of BCR lacking the oligomerization domain, termed Bcr(64-413), that encodes the Ser-Thr protein kinase activity of Bcr. The autokinase product contained a M(r) 45,000-47,000 and 55,000 protein. Both species were detected by a Bcr phosphoserine 354 sequence-specific antibody. In contrast, the S354A mutant of Bcr(64-413), although maintaining autokinase activity, produced only the M(r) 45,000-47,000 kinase product. Abl SH2 binding experiments indicated that the M(r) 55,000 species of Bcr(64-413) but not the M(r) 45,000-47,000 species bound strongly to glutathime transferase-Abl SH2. The S354A mutant of Bcr(64-413) did not bind to glutathime transferase-Abl SH2. An adenovirus encoding Bcr(64-413) S354A did not induce cell death in CML cell lines in contrast to wild-type Bcr(64-413). Our findings indicate that Ser-354 of Bcr is part of a gating mechanism, which, after its phosphorylation, allows structural changes to occur in the Bcr protein. This altered phosphoserine form of the Bcr protein selectively binds to the Abl SH2 domain of the oncoprotein, which we propose down-regulates the activity of the Bcr-Abl tyrosine kinase.

Amino Acid Sequence↗
PubMed2002

Bcr: a negative regulator of the Bcr-Abl oncoprotein in leukemia.

The fusion of 5' parts of the BCR gene to the ABL gene at the second exon yields several forms of an oncogenic Bcr-Abl oncoprotein observed in several types of Philadelphia chromosome positive leukemia patients. The first exon of the BCR gene is a critical part of this fusion, as the coiled-coil domain at the amino terminal domain of the Bcr protein causes oligomerization of the Bcr-Abl oncoprotein forming tetramers, thereby activating the tyrosine kinase activity of the normally silent c-Abl protein. Another consequence of this Bcr-Abl fusion is the extensive autophosphorylation of the cis Bcr protein sequences on tyrosine residues. This review will summarize the effects of Bcr-Abl autophosphorylation on tyrosines as they relate to the oncogenic activity of Bcr-Abl, and as a means to inactivate the serine/threonine kinase activity of the Bcr protein. The review also discusses our findings that show that phosphoserine Bcr by means of a unique structure, binds to the Abl SH2 domain of the Bcr-Abl oncoprotein, and as a result this SH2 binding inhibits the oncogenic effects of the oncoprotein. Our results indicate that one effect of this binding is inhibition of the Bcr-Abl tyrosine kinase. Serine 354 of Bcr plays a major role in this inhibition. In the case of Bcr(64-413), serine 354 is required for the formation of the unique Bcr structure that binds to the Abl SH2 domain.

Amino Acid Sequence↗
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↗
PubMed2002

Interleukin-3 protects Bcr-Abl-transformed hematopoietic progenitor cells from apoptosis induced by Bcr-Abl tyrosine kinase inhibitors.

Bcr-Abl tyrosine kinase has been validated as a molecular target for the treatment of chronic myelogenous leukemia (CML). More recently, it has been reported that CML patients could develop resistance to the Bcr-Abl tyrosine kinase inhibitor, imatinib (STI571, Gleevec), pointing to the need for development of additional Bcr-Abl tyrosine kinase inhibitors or other therapeutic strategies. It was also found that a significant proportion of patients who received the Bcr-Abl inhibitor did not achieve complete cytogenetic response. Mechanisms for incomplete cytogenetic response to Bcr-Abl inhibition are not entirely clear. We report here three new pyrido[2,3-d]pyrimidine Bcr-Abl tyrosine kinase inhibitors, PD164199, PD173952, PD173958, that induced apoptosis of Bcr-Abl-dependent hematopoietic cells. An interleukin-3 (IL-3) autocrine loop was observed previously in primitive CD34(+)/Bcr-Abl(+) leukemic cells in CML patients. Using 32Dp210(Bcr-Abl)and Baf3p210(Bcr-Abl) cells as models, we tested whether IL-3 might protect Bcr-Abltransformed, IL-3-responsive cells from apoptosis caused by Bcr-Abl tyrosine kinase inhibition. Results of trypan blue exclusion, fluoroisothiocyanate-valyl-alanyl-aspartyl-[O-methyl] -fluoromethylketone (FITC-VAD-FMK), and Annexin-V/7-amino-actinomycin D (7-AAD) binding assays indicate that IL-3 could protect Bcr-Abl-transformed, IL-3 responsive hematopoietic progenitor cells from apoptosis induced by Bcr-Abl tyrosine kinase inhibitors. This finding raises the possibility that the IL-3 autocrine loop found in primitive CD34(+)/Bcr-Abl(+) cells in CML patients could contribute to the incomplete eradication of Bcr-Abl(+) cells by Bcr-Abl inhibition.

Annexin A5↗
PubMed1993

Inhibition of phosphorylation of p160 BCR within p210 BCR-ABL complexes during early stages of phorbol ester-induced differentiation of K562 cells.

The kinase activity of the BCR-ABL gene product is known to be down-regulated in K562 cells treated with low concentrations of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). The reduction of BCR-ABL kinase activity is followed by the loss of cell proliferation and progression to a more differentiated state. We have previously demonstrated that K562 cells possess protein complexes that contain p210 BCR-ABL and p160 BCR (M. L. Campbell, W. J. Li, and R. B. Arlinghaus, Oncogene, 5: 773-776, 1990). We performed experiments to determine whether BCR-ABL/BCR complexes were disrupted prior to alterations in cell growth and differentiation effects in TPA-treated K562 cells. Our results indicate that BCR-ABL/BCR complexes disappeared at precisely the same time after TPA treatment as the loss of autophosphorylation activity exhibited by total p210 BCR-ABL, which occurred 16-19 h after TPA treatment. The loss of kinase activity preceded the loss of p210 BCR by more than 24 h. A degraded form of p210 BCR-ABL (about 175 kilodaltons) accounted for the residual autophosphorylation activity seen during the later phases of kinase inactivation following TPA treatment, and this form was preferentially sequestered within BCR-ABL/BCR complexes. This altered BCR-ABL protein, although able to autophosphorylate, had reduced ability to phosphorylate p160 BCR. We conclude that 15 nM TPA treatment of K562 cells initiates effects that simultaneously interfere with the phosphorylation of p160 BCR in BCR-ABL complexes and inactivates the autophosphorylation activity of the full length BCR-ABL protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Differentiation↗