Two bcr/abl fusion gene products, P210bcr/abl and P190bcr/abl, are equally sensitive to the protein tyrosine phosphatase of mature granulocytes.

Two bcr/abl fusion gene products with tyrosine kinase activity have been found in two phenotypes of Philadelphia chromosome (Ph1)-positive leukemia. P210bcr/abl (P210) is associated with Ph1-positive chronic myelogenous leukemia (CML), while P190bcr/abl is associated with Ph1-positive acute leukemia. We compared the susceptibility of 32Pi-labeled P210 from K-562 cells and P190 from MR-87 cells to protein tyrosine phosphatase (PTPase). PTPase, present in the lysate of mature granulocytes from CML patients as well as in the lysate of these cells from normal subjects, effectively dephosphorylated the CML-associated P210 and the acute leukemia associated P190. This PTPase activity was specifically inhibited by ZnCl2; it was not present in lymphocyte lysates, and was not inhibited by neutralization with anti-CD45 antibody. Since P210 and P190 were equally sensitive to the PTPase, the difference in leukemic phenotypes associated with the expression of these two tyrosine kinases cannot be explained by the differential dephosphorylation of P210 and P190.     

The coiled-coil domain and Tyr177 of bcr are required to induce a murine chronic myelogenous leukemia-like disease by bcr/abl

The bcr/abl fusion in chronic myelogenous leukemia (CML) creates a chimeric tyrosine kinase with dramatically different properties than intact c-abl. In P210 bcr/abl, the bcr portion includes a coiled-coil oligomerization domain (amino acids 1-63) and a grb2-binding site at tyrosine 177 (Tyr177) that are critical for fibroblast transformation, but give variable results in other cell lines. To investigate the role of the coiled-coil domain and Tyr177 in promoting CML, 4 P210 bcr/abl-derived mutants containing different bcr domains fused to abl were constructed. All 4 mutants, Delta(1-63) bcr/abl, (1-63) bcr/abl, Tyr177Phe bcr/abl, and (1-210) bcr/abl exhibited elevated tyrosine kinase activity and conferred factor-independent growth in cell lines. In contrast, differences in the transforming potential of the 4 mutants occurred in our mouse model, in which all mice receiving P210 bcr/abl-expressing bone marrow cells exclusively develop a myeloproliferative disease (MPD) resembling human CML. Of the 4 mutants assayed, only 1-210 bcr/abl, containing both the coiled-coil domain and Tyr177, induced MPD. Unlike full-length P210, this mutant also caused a simultaneous B-cell acute lymphocytic leukemia (ALL). The other 3 mutants, (1-63) bcr/abl, Tyr177Phe bcr/abl, and Delta(1-63) bcr/abl, failed to induce an MPD but instead caused T-cell ALL. These results show that both the bcr coiled-coil domain and Tyr177 are required for MPD induction by bcr/abl and provide the basis for investigating downstream signaling pathways that lead to CML.     

Expression of the hybrid P210 bcr/abl protein in Philadelphia chromosome positive B-lymphoid cell lines

An altered c-abl protein (P210) bearing increased tyrosine kinase activity represents the product of the hybrid bcr/c-abl gene arising as a consequence of the Philadelphia (Ph1) chromosome translocation, the consistent cytogenetic abnormality of chronic myelogenous leukemia (CML). Although the chronic phase of this disease is substantially characterized by a marked proliferation of myeloid cells, the Ph1 translocation occurs in an early multipotent stem cell, giving rise to both myeloid and lymphoid cell lineages. Here we show that P210 bcr/abl protein expression varies greatly in different Ph1 chromosome positive B-lymphoid cell lines obtained from Epstein-Barr virus-transformed lymphocytes of a CML patient in the chronic phase. In addition Ph1 positive and Ph1 negative lymphoid cell lines obtained from the same patient were tested for a number of biological properties including the immunophenotype, the capacity to grow in soft agar and possible tumorigenicity in nude mice. No differences were found.     

Consistent involvement of the bcr gene by 9;22 breakpoints in pediatric acute leukemias

To investigate the relationship of bcr-abl fusion mRNAs with childhood acute lymphoblastic leukemias (ALL), we examined 27 pediatric Philadelphia chromosome (Ph1)-positive acute leukemias using a reverse polymerase chain reaction (PCR) procedure. In cells from 24 leukemias, single bcr-abl PCR products were detected that corresponded to breakpoints in the minor breakpoint cluster region (mbcr in intron 1 of the bcr gene) associated with production of the P190 fusion protein. Cells from the three remaining leukemias contained breakpoints in the major breakpoint cluster region (Mbcr) as shown by PCR and Southern blot analyses. These three leukemias also contained low levels of the mbcr PCR product that may have resulted from alternative splicing of the bcr-abl precursor RNA. A screen of 35 additional leukemias from patients who failed therapy before day 180 (induction failures or early relapses) found one case with unsuccessful cytogenetics to express Mbcr-abl RNA. All four children with Mbcr breakpoints had white blood cell levels in excess of 250,000 at presentation (compared with 2 of 24 with mbcr breakpoints) and two had hematologic and clinical features suggestive of chronic myelogenous leukemias (CML) in lymphoid blast crisis. Our results indicate that in Ph1-positive pediatric leukemias, all 9;22 breakpoints occur in one of the two known breakpoint cluster regions in the bcr gene on chromosome 22. The reverse PCR reliably detected all patients with cytogenetic t(9;22) and is capable of detecting additional Ph1-positive leukemias that are missed by standard cytogenetics. Furthermore, the Mbcr-type breakpoint, associated with production of p210, can be seen in childhood leukemias presenting either as clinical ALL or as apparent lymphoid blast crisis of CML, suggesting that t(9;22) breakpoint locations do not exclusively determine the biologic and clinical features of pediatric Ph1-positive ALL.     

Expression of c-abl in Philadelphia-positive acute myelogenous leukemia

The identical cytogenetic marker, t(9;22)(q34;q11) (Philadelphia [Ph] translocation), is found in approximately 90%, 20%, and 2% of adult patients with chronic myelogenous leukemia (CML), acute lymphoblastic leukemia (ALL), and acute myelogenous leukemia (AML), respectively. In CML, the molecular events resulting from the Ph translocation include a break within the bcr locus on chromosome 22, transfer of the c-abl protooncogene from chromosome 9 to 22, and formation of an aberrant 210- kD bcr-abl fusion protein (p210bcr-abl). Recently, the absence of bcr rearrangement and expression of a distinct aberrant 190-kd abl protein (p190c-abl) has been described in Ph-positive ALL, with the suggestion that the two abl variants may be pathogenetically associated with myeloid v lymphoid leukemogenesis. Here we report that the genomic configuration and translation product of Ph-positive AML can be similar to that of Ph-positive ALL: the break at 22q11 may occur outside the 5.8 kb bcr region and result in expression of a 190-kD abl protein lacking these bcr sequences. Phosphokinase enzymatic activity, a fundamental property of p210bcr-abl, was also associated with AML- derived p190c-abl. Our current observations indicate that p190c-abl can be found in cells of lymphoid or myeloid lineage and is therefore unlikely to play a specific role in the development of lymphoid leukemias. Formation of p190c-abl instead of p210bcr-abl appears to be a characteristic of the acute rather than the chronic Ph-positive leukemic state.     

Alpha-interferon reduces in vivo phosphorylation of P210bcr/abl protein during hemin-induced erythroid differentiation of K-562 cells

alpha-Interferon (IFN-alpha) is important in the management of chronic myelogenous leukemia (CML). The P210bcr/abl fusion protein, with enhanced tyrosine kinase activity, is implicated in the pathogenesis and progression of the disease. To elucidate the inhibitory mechanism of IFN-alpha on CML cell proliferation, we studied the effect of IFN-alpha on P210bcr/abl in K-562 cells. The phosphorylated level of P210bcr/abl was not altered by treatment with IFN-alpha alone despite its inhibiting cell proliferation. However, when K-562 cells were treated with either a low (5 x 10(2) U/ml) or high (10(4) U/ml) concentration of IFN-alpha in the presence of hemin, P210bcr/abl protein activity decreased through reduction of in vivo phosphorylation, but not through inhibition of de novo protein synthesis. Furthermore, hemoglobin content was increased by IFN-alpha at both low and high concentrations in tandem with hemin-induced erythroid differentiation and the change in P210bcr/abl. These results demonstrate that IFN-alpha synergises hemin-mediated erythroid differentiation as it reduces the in vivo tyrosine phosphorylation of P210bcr/abl in K-562 cells.     

Differences in tyrosine phosphorylated proteins between cells expressing P210bcr/abl and P190bcr/abl.

We analysed differences between the populations of tyrosine phosphorylated proteins in two cell lines, K-562 and MR-87, which express two different bcr-abl fusion gene products, using both immunoprecipitation and Western blotting with an anti-phosphotyrosine antibody. K-562 cells preferentially expressed P210bcr/abl (P210), while MR-87 expressed P190bcr/abl (P190). Tyrosine phosphorylated proteins with a molecular mass of 150 kDa (p150) and 115 kDa (p110) were found in both K-562 and MR-87. A 36 kDa protein (p36) was tyrosine phosphorylated in vivo only in K-562 cells, while proteins with a molecular mass of 140 kDa (p140) and 62 kDa (p62) were found only in MR-87 cells. Moreover, several proteins in the detergent-insoluble cell fraction were differently tyrosine phosphorylated in vitro in K-562 and MR-87 lysates. These results suggest that P210 and P190 may have different substrates, and thus, different signal transduction pathways for cell proliferation, although the differential association of such cellular proteins with the two bcr/abl products remains to be clarified.     

Clonal evolution in a myeloid cell line transformed to interleukin-3 independent growth by retroviral transduction and expression of p210bcr/abl.

Current evidence suggests that the expression of the tyrosine kinase p210bcr/abl in chronic myelogenous leukemia (CML) may directly induce the initial phase of granulocytic hyperplasia. However, the dysregulation of additional genes appears to be required for transition to the acute leukemic phase, as inferred by the appearance of recurrent secondary cytogenetic abnormalities in the majority of patients. To determine whether the expression of p210bcr/abl alone is responsible for this genetic instability, we introduced and expressed the bcr/abl gene from a retroviral vector in a clone of the interleukin-3 (IL-3) dependent myeloblastic 32D C13(G) cell line. Clonal and polyclonal cells transformed to IL-3 independent growth were observed for a period extending up to 6 months for changes in the expression of p210bcr/abl, cell proliferation, inhibition by prostaglandin E1 (PGE1), forskolin, and cyclic adenosine monophosphate (cAMP) analogues, regulation of the cell cycle, and karyotype. Whereas the properties of control vector infected 32D C13(G)' cells remained stable over time, cells expressing p210bcr/abl were phenotypically unstable. In cells expressing p210bcr/abl, we observed selective modulation of p210bcr/abl mRNA and protein expression, evolution from partial to full abrogation of IL-3 dependence, reduced serum requirements, increased cell proliferation, decreased inhibition by PGE1 and cAMP analogues, and the appearance of new structural and numerical chromosomal abnormalities with successive cell passages. These results indicate that expression of p210bcr/abl can directly predispose 32D C13(G)' cells to genetic instability, promotes the emergence of clones with an increased proliferative advantage, and may represent an in vitro model suitable for the study of mechanisms underlying progression to the acute leukemic phase in CML.     

Expression of p210bcr/abl by metallothionein promoter induced T-cell leukemia in transgenic mice

The p210bcr/abl chimeric protein is considered to be implicated in the pathogenesis of Philadelphia chromosome-positive human leukemias. To investigate its biologic function in vivo, we generated transgenic mice expressing p210bcr/abl driven by the metallothionein enhancer/promoter. Two of six founder mice and the transgenic progeny developed leukemias several months after birth. In the leukemic tissues, the expression of the p210bcr/abl transgene product was detected and the increased tyrosine-phosphorylation of cellular proteins was observed. The expressed p210bcr/abl transgene product was shown to possess an enhanced kinase activity. The leukemic cells showed rearrangements in the T-cell receptor loci, indicating that the leukemic cells were monoclonal and committed to the T-cell lineage. Polymerase chain reaction analysis for tissue distribution of p210bcr/abl expression showed that, in the transgenic line that reproducibly developed leukemias, p210bcr/abl was expressed in the hematopoietic tissues such as thymus and spleen; on the other hand, in the transgenic lines that have not developed leukemias, p210bcr/abl expression was detected only in the nonhematopoietic tissues such as the brain and kidney. These results suggest that the tumorigenicity of the p210bcr/abl chimeric protein is restricted to the hematopoietic tissues in vivo and that an event enhancing p210bcr/abl expression contributed a proliferative advantage to hematopoietic precursor cells and eventually developed T- cell leukemia in transgenic mice.     

Variable expression of the translocated c-abl oncogene in Philadelphia-chromosome-positive B-lymphoid cell lines from chronic myelogenous leukemia patients.

The consistent cytogenetic translocation of chronic myelogenous leukemia (the Philadelphia chromosome, Ph1) has been observed in cells of multiple hematopoietic lineages. This translocation creates a chimeric gene composed of breakpoint-cluster-region (bcr) sequences from chromosome 22 fused to a portion of the abl oncogene on chromosome 9. The resulting gene product (P210c-abl) resembles the transforming protein of the Abelson murine leukemia virus in its structure and tyrosine kinase activity. P210c-abl is expressed in Ph1-positive cell lines of myeloid lineage and in clinical specimens with myeloid predominance. We show here that Epstein-Barr virus-transformed B-lymphocyte lines that retain Ph1 can express P210c-abl. The level of expression in these B-cell lines is generally lower and more variable than that observed for myeloid lines. Protein expression is not related to amplification of the abl gene but to variation in the level of bcr-abl mRNA produced from a single Ph1 template.     

Model mice for BCR/ABL-positive leukemias

p210bcr/abl is detected in almost all chronic myelogenous leukemia (CML) patients and a significant number of acute lymphoblastic leukemia (ALL) cases. It is generated by a reciprocal chromosomal translocation, t(9;22) (q34;q11), and the enhanced kinase activity of the protein is believed to be implicated in the pathogenesis of the diseases. To examine its oncogenicity in vivo and to create an animal model for BCR/ABL-positive leukemias, we generated transgenic mice expressing p210bcr/abl driven by the promoter of the mouse tec gene, a cytoplasmic tyrosine kinase preferentially expressed in early hematopoietic progenitors. While the founder mice showed excessive proliferation of lymphoblasts shortly after birth and were diagnosed as ALL, the transgenic progeny reproducibly exhibited marked granulocyte hyperplasia with thrombocytosis after a long latent period, which closely resembles the clinical course of human CML. In addition, to investigate whether loss of p53 would play a role in the transition from chronic phase to blast crisis of CML, we crossmated p210bcr/abl transgenic (BCR/ABLtg/-) mice with p53 heterozygous (p53+/-) mice and generated p210bcr/abl transgenic, p53 heterozygous (BCR/ABLtg/- p53+/-) mice, in which a somatic alteration in the residual p53 allele directly abrogates p53 function. The BCR/ABLtg/- p53+/- mice exhibited rapid proliferation of blast cells and died in a short period compared with their wild-type (BCR/ABL-/- p53+/+), p53 heterozygous (BCR/ABL-/- p53+/-), and p210bcr/abl transgenic (BCR/ABLtg/- p53+/+) littermates. Interestingly, the normal p53 allele was frequently and preferentially lost in the tumor tissues, providing in vivo evidence that acquired loss of p53 contributes to the blastic transformation of p210bcr/abl-expressing hematopoietic cells. Our transgenic mice will be a useful model for investigating oncogenic properties of p210bcr/abl in vivo and will provide insights into the molecular mechanism(s) underlying the progression from chronic phase to blast crisis of CML.     

老年白血病bcr/abl融合基因的表达及其临床意义

目的　观察bcr/abl融合基因在老年白血病的表达及其临床意义。　 方法 　应用逆转录聚合酶链反应 (RT PCR)一步法检测 62例老年白血病患者bcr/abl融合基因的表达。　 结果 　 62例患者中bcr/abl融合基因阳性 5 3例 ,阳性率 85 5 % ,其中急性淋巴细胞白血病 (ALL) 17例 ,阳性 9例 (5 2 9% ) ;慢性粒细胞白血病 (CML)45例 ,阳性 44例 (97 88% )。DOCP方案治疗 7例bcr/abl ALL患者完全缓解 (CR)率 2 8 6% ,6例bcr/abl-ALL患者CR率 66 7% (P <0 0 1)。　 结论　bcr/abl融合基因检测有助于CML和ALL的临床诊断、治疗选择、微小残留病变 (MRD)监测以及预后判断 ;老年ALLbcr/abl融合基因阳性率较高 ,可能是其治疗效果较差的原因之一 ;bcr/abl ALL患者CR率明显低于bcr/abl-ALL患者 ;RT PCR一步法特异性好、敏感性高、简便快速 ,尤其适用于MRD的临床监测。     

造血干细胞移植后白血病细胞染色体核型和bcr/abl融合基因表达观察

目的：探讨造血干细胞移植(HSCT)后白血病细胞染色体核型和基因表达观察的意义。方法：用骨髓细胞短期培养法和直接法G显带分析染色体；双色荧光原位杂交检测bcr／abl融合基因。结果：2例供者为女性的男性急性髓细胞白血病(AML)患者异体外周血干细胞移植(allo-PBSCT)后染色体检测持续46，XX。最长生存50个月。4例慢性髓细胞白血病(CML)经allo-PBSCT后，Ph染色体和bcr／abl融合基因阳性1例，经供者淋巴细胞输注加干扰素治疗，已生存70个月。Ph染色体阴性bcr／abl融合基因阳性2例，最长生存27个月。Ph染色体阳性bcr／abl融合基因阴性1例，已生存14个月。2例AML自体造血干细胞移植后检测出非特征性染色体畸变，复发后再化疗达完全缓解，最长生存期达81个月。结论：造血干细胞移植后白血病细胞遗传学检测可观察近期疗效，指导后续治疗选择。     

The correlation of breakpoint cluster region rearrangement and p210 phl/abl expression with morphological analysis of Ph-negative chronic myeloid leukemia and other myeloproliferative diseases

The chromosome 22 derivative, the Philadelphia (Ph) chromosome, results from a reciprocal translocation t(9;22) (q34;q11) and is associated with chronic myeloid leukemia (CML). The translocation can be identified at the DNA level in Ph-positive CML by using a probe to the breakpoint cluster region (bcr). In addition, as a result of this translocation an abl-related 210-kd protein with protein tyrosine kinase (PTK) activity is produced. We analyzed 28 cases of Ph-negative CML for rearrangement of the chromosome 22 sequences and found that eight of the 28 show rearrangement of the bcr. When 12 of the Ph-negative cases were independently reviewed, five were indistinguishable from Ph-positive CML on the basis of morphology, peripheral blood film and clinical details. These five also showed bcr rearrangement. The other seven were reclassified as six atypical CML (aCML) and one chronic myelomonocytic leukemia (CMML). None of these seven showed bcr rearrangement. In addition 11 cases of bcr- CML were assayed for abl-related PTK, and no detectable activity was present, whereas p210 phl/abl PTK was observed both in Ph-positive (three cases examined) and Ph-negative, bcr + (four cases examined) CML. Therefore, bcr + CML, whether or not the Ph chromosome is cytogenetically apparent, involves a similar molecular alteration and produces the 210-kd protein with enhanced PTK activity. Furthermore, these cases can be distinguished from Ph-negative bcr- CML by careful evaluation of clinical and hematologic data.     

Molecular analysis of clonality and bcr rearrangements in Philadelphia chromosome-positive acute lymphoblastic leukemia

Philadelphia chromosome (Ph1)-positive chronic myelogenous leukemia (CML) patients consistently show a rearrangement in a 5.8-kilobase length of chromosome 22, referred to as the breakpoint cluster region (bcr). In Ph1-positive acute lymphoblastic leukemia (ALL), the breakpoint in chromosome 22 is more heterogeneous and, in some instances, does not occur within this region. In such cases the cell of origin of the neoplastic clone and the relationship of the disease to CML has remained obscure. We have analyzed the bcr rearrangement in the malignant cells from three patients who presented with Ph1-positive ALL and who in cytogenetic studies had shown evidence of variable involvement of myeloid cells in the Ph1-positive clone. Rearrangements in bcr typical of most cases of CML were detected in purified granulocyte preparations from two of the ALL patients (nos. 1 and 2) and in the blasts from patient 3 at the time of her terminal relapse. In the same analysis the simultaneously obtained granulocytes from patient 3, however, did not show any evidence of bcr rearrangement. Patient 3 was also heterozygous for the BamHI polymorphism in the X- linked hypoxanthine phosphoribosyltransferase (HPRT) gene, thus permitting a different method of clonal analysis based on methylation differences in active and inactive alleles. When DNA from her granulocytes that had shown no bcr rearrangement was hybridized to an HPRT probe, a pattern typical of a polyclonal population was seen. A similar pattern was exhibited by her marrow fibroblasts. In marked contrast, her simultaneously isolated blasts showed an unambiguous monoclonal pattern. These findings demonstrate the origin of the disease in the first two patients in a cell with myelopoietic as well as lymphopoietic potential and confirm the restricted lymphoid cell origin of the neoplastic clone in the third Ph1-positive ALL patient. Furthermore, they indicate that different target cells for transformation within the hematopoietic system may be affected by very similar bcr rearrangements.     

Blast crisis in a murine model of chronic myelogenous leukemia.

The P210bcr/abl protein is produced in cells from patients with Philadelphia chromosome-positive chronic myelogenous leukemia (CML). Retroviral transfer of the gene encoding P210bcr/abl into murine bone marrow induces a granulocytic leukemia that models the chronic phase of human CML. We have transferred the leukemic clone to syngeneic animals, albeit with surprising inefficiency, and have observed CML and clonally related acute leukemias of lymphoid or myeloid phenotype in some transplant recipients. These data show that murine CML can result from retroviral transfer of the bcr/abl gene into pluripotent hematopoietic stem cells, that infected clones repopulate poorly after adoptive transfer, and that these clones can give rise to acute leukemia, reflecting evolution to a phase resembling blast crisis in the human disease.