A novel c-abl protein product in Philadelphia-positive acute lymphoblastic leukaemia

Philadelphia chromosome-positive leukaemia: the translocated genes and their gene products

Overwhelming evidence indicates a role for the deregulated ABL protein tyrosine kinase in the aetiology of CML and Ph-positive acute leukaemia. These disorders are characterized by the generation of BCR/ABL fusion proteins with elevated tyrosine kinase activity. Although much is known concerning the transforming potential of ABL proteins in various systems, very little is understood of the normal function and mode of regulation of ABL activity. The mechanism of oncogenic activation is therefore also obscure. In spite of this, our understanding of the molecular details of these chromosomal translocations allows the design of therapies directed against their unique, leukaemia-specific proteins and RNA products.

Cytogenetic abnormalities in childhood acute lymphoblastic leukemia correlates with clinical features and treatment outcome

Virtually all cases of childhood acute lymphoblastic leukemia have chromosomal abnormalities. Non-random chromosomal abnormalities have been correlated with leukemic cell lineage, the degree of cell differentiation and certain clinical and biologic features. Cytogenetic findings have prognostic significance, but the adverse influence of many rearrangements, including most chromosomal translocations, may be offset by the greater cytoreductive effects of intensified therapy. Cytogenetic abnormalities have also provided focus for molecular studies of leukemogenesis. Such studies have recently identified key genes and their protein products which play important roles in malignant transformation and proliferation.

c-abl has a sequence-specific enhancer binding activity

The enhancers of several distinct viruses contain a common functional element, termed EP. This element binds ubiquitous cellular proteins and generates specific complexes in gel retardation analysis. Ultraviolet cross-linking and Southwestern analysis showed that a 140 kd polypeptide is the major EP DNA-binding protein. Using a combination of DNA binding and immunological techniques, we have identified the c-abl protein in a nuclear complex that binds to the EP element. abl was found to have both a specific and high affinity DNA binding activity. The ability to bind DNA is abolished in the mutant abl protein, p210bcr-abl, consistent with its cytoplasmic localization in chronic myelogenous leukemia.

A 41-kilodalton protein is a potential substrate for the p210bcr-abl protein-tyrosine kinase in chronic myelogenous leukemia cells

Chronic myelogenous leukemia (CML) is characterized by a translocation involving the c-abl protein-tyrosine kinase gene. A chimeric mRNA is formed containing sequences from a chromosome 22 gene (bcr) at its 5' end and all but the variable exon 1 of c-abl sequence. The product of this mRNA, p210bcr-abl, has constitutively high protein-tyrosine kinase activity. We examined K562 cells and other lines established from CML patients for the presence of phosphotyrosine (P-Tyr)-containing proteins which might be p210bcr-abl substrates. Two-dimensional gel separation of 32P-labeled proteins followed by phosphoamino acid analysis of 25 phosphoproteins, which comprised the major alkali-stable phosphoproteins, indicated that three related proteins of 41 kDa are the most prominent P-Tyr-containing proteins detected by this method. The 41-kDa phosphoproteins are found in two other CML lines that we examined but not in lines of similar lineage isolated from patients with distinct leukemic disease. A protein that comigrates with the major form of pp41 (pp41A) and contains P-Tyr is also found in murine fibroblasts and B-lymphoid cells transformed by Abelson murine leukemia virus, which encodes the v-abl protein, and in platelet-derived growth factor-treated fibroblasts, in which it has been described previously. We analyzed three pairs of Epstein-Barr virus-immortalized B-cell lines from individual CML patients and found that only the lines in which active p210bcr-abl was present contained detectable pp41. We also performed immunoblotting with anti-P-Tyr antibodies on the same CML cell lines and detected at least four other putative substrates of p210bcr-abl, which were undetected with use of the two-dimensional gel technique.

Cytogenetic and molecular studies of the Philadelphia translocation in myelodysplastic syndromes. Report of two cases and review of the literature

We report two patients with a myelodysplastic syndrome and the Philadelphia (Ph) chromosome. The first patient was a 73-year-old man who was diagnosed as having a chronic myelomonocytic leukemia in combination with features suggestive of a myeloproliferative syndrome. Chromosomal analysis showed a normal karyotype in the majority of cells, mixed with metaphases containing a standard Ph translocation, t(9;22)(q34;q11), as well as a translocation between chromosome 4 and 6: t(4;6)(p15;p12). Southern blot analysis showed breakpoint cluster region rearrangement as observed in classic chronic myeloid leukemia. The second patient was a 63-year-old man with a myelodysplastic syndrome, type refractory anemia. Cytogenetic study of bone marrow cells at the time of diagnosis revealed a normal karyotype: 46,XY. The initial myelodysplastic syndrome evolved to a myeloproliferative phase with progressive leukocytosis and thrombocytosis. During the terminal phase the Ph chromosome was discovered in 100% of the examined cells. We discuss the correlation between MDS and myeloproliferative diseases, the de novo acquisition of the Ph chromosome during the course of a myelodysplastic syndrome, and review the literature.

T-cell immunity to the joining region of p210BCR-ABL protein

The hallmark of chronic myelogenous leukemia is the translocation of the human c-abl protooncogene (ABL) from chromosome 9 to the specific breakpoint cluster region (bcr) of the BCR gene on chromosome 22. The t(9;22)(q34;q11) translocation results in the formation of a BCR-ABL fusion gene that encodes a 210-kDa chimeric protein with abnormal tyrosine kinase activity. The ABL and BCR genes are expressed by normal cells and thus the encoded proteins are presumably nonimmunogenic. However, the joining-region segment of the p210BCR-ABL chimeric protein is composed of unique sequences of ABL amino acids joined to BCR amino acids that are expressed only by malignant cells. The current study demonstrates that the joining region of BCR-ABL protein is immunogenic to murine T cells. Immunization of mice with synthetic peptides corresponding to the joining region elicited peptide-specific, CD4+, class II major histocompatibility complex-restricted T cells. The BCR-ABL peptide-specific T cells recognized only the combined sequence of BCR-ABL amino acids and not BCR or ABL amino acid sequences alone. Importantly, the BCR-ABL peptide-specific T cells could recognize and proliferate in response to p210BCR-ABL protein. The response of peptide-specific T cells to protein demonstrated that p210BCR-ABL can be processed by antigen-presenting cells so that the joining segment is bound to class II major histocompatibility complex molecules in a configuration similar to that of the immunizing peptide and in a concentration high enough to stimulate the antigen-specific T-cell receptor. Thus, BCR-ABL protein represents a potential tumor-specific antigen related to the transforming event and shared by many individuals with chronic myelogenous leukemia.

A 41-kilodalton protein is a potential substrate for the p210bcr-abl protein-tyrosine kinase in chronic myelogenous leukemia cells

Chronic myelogenous leukemia (CML) is characterized by a translocation involving the c-abl protein-tyrosine kinase gene. A chimeric mRNA is formed containing sequences from a chromosome 22 gene (bcr) at its 5' end and all but the variable exon 1 of c-abl sequence. The product of this mRNA, p210bcr-abl, has constitutively high protein-tyrosine kinase activity. We examined K562 cells and other lines established from CML patients for the presence of phosphotyrosine (P-Tyr)-containing proteins which might be p210bcr-abl substrates. Two-dimensional gel separation of 32P-labeled proteins followed by phosphoamino acid analysis of 25 phosphoproteins, which comprised the major alkali-stable phosphoproteins, indicated that three related proteins of 41 kDa are the most prominent P-Tyr-containing proteins detected by this method. The 41-kDa phosphoproteins are found in two other CML lines that we examined but not in lines of similar lineage isolated from patients with distinct leukemic disease. A protein that comigrates with the major form of pp41 (pp41A) and contains P-Tyr is also found in murine fibroblasts and B-lymphoid cells transformed by Abelson murine leukemia virus, which encodes the v-abl protein, and in platelet-derived growth factor-treated fibroblasts, in which it has been described previously. We analyzed three pairs of Epstein-Barr virus-immortalized B-cell lines from individual CML patients and found that only the lines in which active p210bcr-abl was present contained detectable pp41. We also performed immunoblotting with anti-P-Tyr antibodies on the same CML cell lines and detected at least four other putative substrates of p210bcr-abl, which were undetected with use of the two-dimensional gel technique.

Evolution of Ig- and T-cell receptor gene configuration in a Ph1+ hybrid leukemia patient

In a longitudinal study of a 32-year-old male with Ph1+ hybrid leukemia we have followed the immunophenotype and configuration of Ig- and TCR genes during the course of different chemotherapy regimens directed first against the myeloid and later against the lymphoid components of the disease. We identified changes in all parameters, interpretable as an evolution of the malignant clone resulting in a leukemic switch towards a more lymphoid character. Thus, while the expression of the myeloid antigens CD13 and CD33 decreased, that of CD10 (CALLA) and CD20 (B1) increased. Moreover, while the configuration of the Ig heavy and light chain lambda genes remained constant during the whole period of treatment, that of the Ig light chain kappa gene and TCR beta gene displayed extensive rearrangements after initiation of ALL therapy. Since this patient represents a de novo acute leukemia as evaluated by location of the translocation-breakpoint on chromosome 22, our data clearly indicate that Ig- and TCR gene rearrangements might prove a valuable addition in monitoring Ph1+ hybrid leukemias, providing guidelines for optimizing chemotherapy.

Oncogenes and tumor suppressor genes: new biochemical tests

Oncogenes and tumor suppressor genes are genes involved in cell proliferation and differentiation. They play a crucial role in the initiation and progression of cancer. Some of these genes are found to be altered in human cancers, i.e., mutated, amplified, deleted, translocated, or abnormally regulated. Recently, the protein products of the genes have been purified, and antibodies against them have been developed. Studies of oncogenes and tumor suppressor genes at the DNA, mRNA, or protein level may reveal new ways for diagnosis, monitoring, prognosis, and treatment of cancer. In this article, the area of oncogenes and tumor suppressor genes is reviewed, with emphasis on clinical applications and biochemical testing. Although most of the currently known genetic markers are not sufficiently specific or sensitive, it is anticipated that the discovery of newer markers and the application of new analytical techniques may help in devising biochemical testing suitable for screening and early diagnosis of malignant diseases.

Diagnostic utility of oncogenes and their products in human cancer

The first clear cut association of an oncogene with a specific cancer is the c-abl translocation in chronic myelogenous leukemia and acute lymphocytic leukemia; it has been observed in 90% of CML cases examined. This is the major contributing factor to its being the target of the first oncogene-based FDA-approved diagnostic test. Although the role of the abl translocation in the tumorigenic process is not yet understood, it is clear that somehow it must be causally related to the disease, and thus is an ideal target for a diagnostic test. The association of this oncogene with a specific cancer is the model on which all others may be based in the future. Second generation tests could easily include PCR on mRNA, and/or in situ hybridization, both of which could be performed using blood samples. Both methods would provide a faster means of testing a large number of cells, however, the methodologies must be improved through automation and computer-aided image analysis, respectively, in order to become useful routine tests. Both neu and epidermal growth factor receptor (EGFR) appear to have a close correlation between overexpression of the gene product and outcome of disease in breast cancer; valuable information for prognosis of the disease. And again, although the actual mechanism of action of these molecules and how this relates to the tumorigenic process is not yet known, it is believed from the very nature of the molecules that they must in some way contribute to the progression of the disease. In both cases, the protein products are overexpressed in tissue, and in the case of Neu, it appears as through at least some of the patients have a Neu-related protein in their serum. These molecules present relatively easy targets for the development of diagnostic/prognostic assays, as antibodies are easily made and can be incorporated into a variety of assay formats. Current assays available, an ELISA for Neu and a radio-ligand binding assay for EGFR, are highly sensitive, reproducible and relatively easy to perform. Only the ELISA is commercially available, however, and hence allows for easy comparison between laboratories. An abvious step towards the routine measurement of EGFR then is the development of a comparable commercially available test. An improvement for both types of assay would be the incorporation of an internal control to gauge the cellular component of the tissue samples that are tested. The outcome of the applications of myc and ras to cancer diagnostics is not so easily predictable, with a couple of exceptions.(ABSTRACT TRUNCATED AT 400 WORDS)

Molecular studies of chronic myelogenous leukemia using the polymerase chain reaction

Thirty-two cases of chronic myelogenous leukemia (CML) were studied to determine whether there was a correlation between the position of the chromosome breakpoint within the breakpoint cluster region (bcr) on chromosome 22 and the type of chimeric mRNA expression. One case with the chromosome breakpoint in zone 2 of the major bcr (Mbcr) and six cases with breakpoints in zone 3 expressed Mbcr exon 2-abl (b2-a) mRNA, and they were in distinguishable at the level of mRNA expression. The remaining ten cases with breakpoints in zone 3 and all ten cases with breakpoints in zone 4 expressed Mbcr exon 3-abl (b3-a) mRNA with or without b2-a mRNA. Three cases with breakpoints in zone 5 expressed b3-a mRNA, and none of these expressed Mbcr exon 4-abl(b4-a) mRNA. The cases with breakpoints in zones 4 or 5 had b3-a mRNA expression indistinguishable from those with breakpoints in zone 3. In two patients, the breakpoint in the bcr could not be determined by Southern hybridization using the 3' bcr probe or the large bcr probe. However, when analyzed for chimeric mRNA expression, both of them exhibited b3-a chimeric mRNA, suggesting the possibility that the entire Mbcr is deleted in the majority of leukemic cells in these patients. These studies indicate that Southern hybridization analysis combined with the polymerase chain reaction assay is a useful approach to understanding the pathologic role of bcr-abl gene recombination and expression in the development of CML.

The BCR gene encodes a novel serine/threonine kinase activity within a single exon

Sequences encoded by the first exon of BCR that bind to the ABL SH2 domain are essential for the activation of the ABL tyrosine kinase and transforming potential of the chimeric BCR-ABL oncogene. The normal cellular BCR gene encodes a 160,000 dalton phosphoprotein associated with a serine/threonine kinase activity, but it shows only weak dispersed homologies to protein kinases. p160c-BCR was purified to apparent homogeneity as an oligomer of greater than 600,000 daltons that contains autophosphorylation activity and transphosphorylation activity for several protein substrates. A region containing paired cysteine residues within the 426 amino acids encoded by the first exon of BCR is essential for its novel phosphotransferase activity, which overlaps with the strong SH2-binding regions. The recent demonstration of a GTPase-activating function within the C-terminal portion of BCR suggests that the protein kinase and SH2-binding domains may work in concert with other regions of the molecule in intracellular signalling processes.

Mice homozygous for the ablm1 mutation show poor viability and depletion of selected B and T cell populations

The c-abl gene, originally identified as the cellular homolog of the transforming gene of the Abelson murine leukemia virus, encodes a protein-tyrosine kinase of unknown function that is expressed in all mammalian tissues. We have previously described the introduction of a mutation in the c-abl gene into the mouse germline via targeted gene disruption of embryonic stem cells. We now show that mice homozygous for this mutation are severely affected, displaying increased perinatal mortality, runtedness, and abnormal spleen, head, and eye development. We have examined components of the immune system and have found major reductions in B cell progenitors in the adult bone marrow, with less dramatic reductions in developing T cell compartments.

Activation of tyrosinase kinase and microfilament-binding functions of c-abl by bcr sequences in bcr/abl fusion proteins

Chronic myelogenous leukemia and one type of acute lymphoblastic leukemia are characterized by a 9;22 chronosome translocation in which 5' sequences of the bcr gene become fused to the c-abl proto-oncogene. The resulting chimeric genes encode bcr/abl fusion proteins which have deregulated tyrosine kinase activity and appear to play an important role in induction of these leukemias. A series of bcr/abl genes were constructed in which nested deletions of the bcr gene were fused to the c-abl gene. The fusion proteins encoded by these genes were assayed for autophosphorylation in vivo and for differences in subcellular localization. Our results demonstrate that bcr sequences activate two functions of c-abl; the tyrosine kinase activity and a previously undescribed microfilament-binding function. Two regions of bcr which activate these functions to different degrees have been mapped: amino acids 1 to 63 were strongly activating and amino acids 64 to 509 were weakly activating. The tyrosine kinase and microfilament-binding functions were not interdependent, as a kinase defective bcr/abl mutant still associated with actin filaments and a bcr/abl mutant lacking actin association still had deregulated kinase activity. Modification of actin filament functions by the bcr/abl tyrosine kinase may be an important event in leukemogenesis.

Activation of tyrosinase kinase and microfilament-binding functions of c-abl by bcr sequences in bcr/abl fusion proteins

Chronic myelogenous leukemia and one type of acute lymphoblastic leukemia are characterized by a 9;22 chronosome translocation in which 5' sequences of the bcr gene become fused to the c-abl proto-oncogene. The resulting chimeric genes encode bcr/abl fusion proteins which have deregulated tyrosine kinase activity and appear to play an important role in induction of these leukemias. A series of bcr/abl genes were constructed in which nested deletions of the bcr gene were fused to the c-abl gene. The fusion proteins encoded by these genes were assayed for autophosphorylation in vivo and for differences in subcellular localization. Our results demonstrate that bcr sequences activate two functions of c-abl; the tyrosine kinase activity and a previously undescribed microfilament-binding function. Two regions of bcr which activate these functions to different degrees have been mapped: amino acids 1 to 63 were strongly activating and amino acids 64 to 509 were weakly activating. The tyrosine kinase and microfilament-binding functions were not interdependent, as a kinase defective bcr/abl mutant still associated with actin filaments and a bcr/abl mutant lacking actin association still had deregulated kinase activity. Modification of actin filament functions by the bcr/abl tyrosine kinase may be an important event in leukemogenesis.

Studies of BCR rearrangements in Philadelphia-positive acute leukemia

Five patients with Philadelphia-positive acute leukemia were cytogenetically and molecularly investigated in order to determine the localization of the breakpoints on chromosome 22. Rearrangements of the bcr segment were detected in one case with acute mixed leukemia in a child. Rearrangements in the BCR gene first intron, the so-called bcr2 and bcr3 regions, were detected in two other cases, one with an acute lymphoblastic leukemia (ALL) and one with mixed acute leukemia. No molecular rearrangement could be detected in the last two cases, an ALL and a T-cell acute lymphoblastic leukemia with a t(2;22) translocation.

Unique organization of the human BCR gene promoter

The promoter of the human BCR gene, regulating the transcription of the chimeric BCR/ABL mRNA in leukemia, has been isolated and characterized. A region of 1.1 kb immediately 5' to the transcription start site was analyzed in detail by sequencing, DNase 1 footprinting, gel retardation and functional studies. These experiments localized a minimal promoter to a 650 bp sequence, composed of 270 bp of 5' flanking sequences and 380 bp of exon 1 transcribed sequences. The promoter region includes a TTTAA box, one Sp1 site and a novel protein-binding sequence absolutely necessary for efficient transcription in vivo. Six additional protein-binding regions were identified more to the 5'. Of these, one is found in an inverted repeat in the 3' coding and splice donor region of BCR exon 1.

Philadelphia chromosome positive B-cell type malignant lymphoma expressing an aberrant 190 kDa bcr-abl protein

The Philadelphia (Ph) chromosome translocation, t(9:22) (q34;q11) is found in some acute lymphoid leukaemias (ALL) and acute myeloid leukaemias (AML). Although cytogenetically all pH chromosomes appear similar, the 22q11 breakpoints found in acute leukaemias are of two kinds, those within the major breakpoint cluster region (Mbcr-1) of the BCR gene as found in chronic myelogenous leukaemia (CML), and those within the first intron of this gene. In the former group the molecular events are the same as those found in CML, p210 bcr-abl, encoded by 8.5 kb mRNA; however, a new aberrant protein, p190 bcr-abl, is found in the latter group. Ph translocation is also found in a few cases with malignant lymphoma, but it has not been characterized at the molecular level. We describe here a non-Hodgkin's lymphoma case with primary splenic presentation, which showed a complex Ph translocation. Neoplastic cells were of a B-cell origin (HLA-DR+, sIgM+, sIg lambda +, CALLA-). Molecular studies revealed the expression of p190 bcr-abl with no Mbcr-1 rearrangement. Our case indicates that the same Ph translocation as seen in acute leukaemias can be found in haematologic disorders other than leukaemias, suggesting that a c-abl gene activating mechanism may be involved in the pathogenesis of wide spectrum of haematologic malignancies.

Molecular biology and leukaemia diagnosis

The diagnosis and classification of leukaemia started with simple morphological examination and now embraces use of special stains, cytochemistry and immunophenotyping. Genetic studies have progressed from karyotyping to detection of genetic changes within genes. The methods described in this chapter are still at an early stage of development and, so far, have provided relatively little in the way of an extension of available diagnostic information. Sometimes the methods provide extensions to existing techniques, for example by the detection of bcr rearrangements in patients who have CML or ALL but do not have a detectable Philadelphia chromosome. Another example is retrospective diagnosis of gene rearrangements using DNA from slide preparations. However, it should be noted that it has only very recently been shown that there is likely to be a causal relationship between the Ph chromosome and leukaemia. Daley et al (1990) induced CML in mice by bone marrow transplantation of cells infected with a retrovirus encoding P210bcr/abl and Heisterkamp et al (1990) produced mice transgenic for a BCR/ABL P190 DNA construct and showed that the progeny died of acute leukaemia (mostly ALL). We have not summarized studies of the incidence of activated oncogenes such as RAS in leukaemia and myelodysplasia. Such oncogenes appear to be involved in many tumours and may well indicate either a predisposition to cancer or a particular stage of malignancy, but their analysis does not at present help in making a diagnosis. It is likely that, as we understand more about the nature of the malignant process, we shall be able to use genetic techniques to enhance considerably both diagnostic and prognostic precision.

ABL proteins in Philadelphia-positive acute leukaemias and chronic myelogenous leukaemia blast crises

The Philadelphia chromosome (Ph1) is present in 95% of chronic myelogenous leukaemias (CML) and 15% of acute lymphoblastic leukaemias (ALL). This cytogenetic marker is due to a t(9;22) translocation, which causes a rearrangement of the ABL oncogene. In order to better define the relationship between type of genomic rearrangement, variant ABL protein expressed and haematological phenotype, a series of Ph1-positive acute leukaemias, both myeloblastic (AML) and lymphoblastic, and several CML lymphoid blast crises have been analysed at the DNA and protein level. The results confirm the presence of the ABL protein P210 in all cases of CML, ALL and AML positive for rearrangement in the bcr region of chromosome 22, and, surprisingly, in one AML case apparently negative for bcr rearrangement. The ABL protein P190 was found to be present only in cases of ALL negative for bcr rearrangement. Polymerase chain reaction (PCR) analysis of the types of 9/22 junctions present in the mRNA of CML lymphoid blast crises showed no evidence of 'ALL-type' transcripts.

Late-appearing Philadelphia chromosome in acute lymphoblastic leukemia

We describe the cytogenetic analysis of a patient affected by a common acute lymphoblastic leukemia, L2 type. At diagnosis and first relapse, the karyotype was normal, whereas at the second relapse more than 60% of the examined cells showed a Philadelphia chromosome, without any change in the morphological and immunophenotypical picture. This case confirms the observation that leukemic cells are susceptible to developing a Ph, considered a primary chromosomal abnormality, during the course of the disease.

bcr rearrangements in Philadelphia chromosome-positive acute lymphoblastic leukemia. A study of five Chinese patients in Taiwan

Cytogenetic studies were successfully conducted on 73 Chinese patients with acute lymphoblastic leukemia (ALL). A Philadelphia chromosome (Ph) was identified in four (9%) of the 46 children and in four (15%) of the 27 adults. None of these patients had any clinical features suggestive of chronic myelogenous leukemia (CML). Leukemic cells from five of the eight Ph-positive (Ph+) ALL patients were analyzed for bcr rearrangement by Southern blot analysis with three restriction enzymes and two bcr probes. One of the three children and both adult patients studied showed bcr rearrangement. Based on the data from the literature and the present study, 58% of adult and 14% of childhood Ph+ ALL patients demonstrated bcr rearrangement. There were no significant differences in clinical or laboratory findings between the two groups of patients with or without bcr rearrangement. Patients who had Ph+ ALL but no bcr rearrangement appear to have been victims of de novo acute leukemia, but it was still difficult to determine whether patients with bcr rearrangement had acute lymphoid transformation of subclinical CML. More studies and longer follow-ups are needed for clarification.

Lymphoid and mesenchymal tumors in transgenic mice expressing the v-fps protein-tyrosine kinase

src, abl, and fps/fes are prototypes for a family of genes encoding nonreceptor protein-tyrosine kinases. The oncogenic potential of the v-fps protein-tyrosine kinase was investigated by introduction of the gag-fps coding sequence of Fujinami sarcoma virus into the mouse germ line. Transgenic mice with v-fps under the transcriptional control of a 5' human beta-globin promoter (GF) or with both 5' and 3' beta-globin regulatory sequences (GEF) were viable. Unexpectedly, both GF and GEF transgenes were expressed in a wide variety of tissues and induced a spectrum of benign and malignant tumors. These tumors, which included lymphomas, thymomas, fibrosarcomas, angiosarcomas, hemangiomas, and neurofibrosarcomas, developed with various frequencies after latent periods of 2 to 12 months. The majority of lymphoid neoplasms appeared to be of T-cell origin and were monoclonal, as judged by rearrangements of the T-cell receptor beta or immunoglobulin genes. Some tissues that expressed the v-fps oncogene, such as heart, brain, lung, and testes, developed no malignant tumors. The v-fps protein-tyrosine kinase therefore has a broad but not unrestricted range of oncogenic activity in cells of lymphoid and mesenchymal origin. The incomplete penetrance of the neoplastic phenotype and the monoclonality of lymphoid tumors suggest that tumor formation in v-fps mice requires genetic or epigenetic events in addition to expression of the P130gag-fps protein-tyrosine kinase.

Characterization of the translocation breakpoint sequences in Philadelphia-positive acute lymphoblastic leukemia

We have previously described a patient in whom the breakpoint occurred within the first intron of the BCR gene and have cloned the 9q+ and 22q- junctions. We have now determined the nucleotide sequence around the breakpoints on both translocation products from this patient as well as the corresponding regions from the normal chromosomes 9 and 22. We have compared the sequence with that of the breakpoint regions in the Ph1-positive leukemic patients in order to check for the presence of conserved motifs. A + T-rich sequences and ALU repeat elements are the only sequence characteristics which appear to be very common around translocation regions. The chromosome 9 ABL sequences at or adjacent to the breakpoints present in the 22q- product show homology to the consensus ALU sequence while the chromosome 22 sequences do not, suggesting a non-homologous recombination mechanism. While no sequences are deleted, there is a two-base-pair "homology" at the junction. Therefore, staggered breaks followed by ligation and repair could be part of the mechanism involved in the process of translocation in some cases of Ph1-positive ALL.

Acute T-lymphocytic leukemia with Ph1 and 5q-chromosome abnormalities and rearrangements of bcr and TCR-delta genes

Almost all cases of Ph1-positive acute lymphocytic leukemia (ALL) have an immature B-cell phenotype and are CD10-positive. A very rare case of Ph1-positive ALL with T-cell features (T-ALL) is presented. Cytogenetic analyses revealed a clone with a Ph1 chromosome and 5q- at diagnosis, and mosaic clones with an additional complex abnormal karyotype at relapse. DNA analysis revealed rearrangement of the breakpoint cluster region (bcr) gene with deletion of the 5' side and of the T-cell receptor (TCR) delta gene, without any rearrangement of other immune-associated genes. From the results of immunophenotypic and genetic analyses, the origin of leukemic cells seemed to be an immature T-cell at a very early stage on T-cell ontogeny.

Lymphoid and mesenchymal tumors in transgenic mice expressing the v-fps protein-tyrosine kinase

src, abl, and fps/fes are prototypes for a family of genes encoding nonreceptor protein-tyrosine kinases. The oncogenic potential of the v-fps protein-tyrosine kinase was investigated by introduction of the gag-fps coding sequence of Fujinami sarcoma virus into the mouse germ line. Transgenic mice with v-fps under the transcriptional control of a 5' human beta-globin promoter (GF) or with both 5' and 3' beta-globin regulatory sequences (GEF) were viable. Unexpectedly, both GF and GEF transgenes were expressed in a wide variety of tissues and induced a spectrum of benign and malignant tumors. These tumors, which included lymphomas, thymomas, fibrosarcomas, angiosarcomas, hemangiomas, and neurofibrosarcomas, developed with various frequencies after latent periods of 2 to 12 months. The majority of lymphoid neoplasms appeared to be of T-cell origin and were monoclonal, as judged by rearrangements of the T-cell receptor beta or immunoglobulin genes. Some tissues that expressed the v-fps oncogene, such as heart, brain, lung, and testes, developed no malignant tumors. The v-fps protein-tyrosine kinase therefore has a broad but not unrestricted range of oncogenic activity in cells of lymphoid and mesenchymal origin. The incomplete penetrance of the neoplastic phenotype and the monoclonality of lymphoid tumors suggest that tumor formation in v-fps mice requires genetic or epigenetic events in addition to expression of the P130gag-fps protein-tyrosine kinase.

Analysis of BCR-ABL mRNA in chronic myelogenous leukemia patients and identification of a new BCR-related sequence in human DNA

The Philadelphia chromosome is present in more than 95% of chronic myelogenous leukemia patients and in up to 25% of patients with acute lymphocytic leukemia. The major consequence of the aberration is the fusion of the ABL and BCR genes. The position of the breakpoint on chromosome 22 determines which species of the potential three fused mRNAs and proteins will be synthesized. We have used the polymerase chain reaction (PCR) to detect these mRNAs in 53 patients and cell lines and found that around 20% contain simultaneously two BCR-ABL mRNAs, presumably due to a process of alternative splicing. The results also indicate that most patients in lymphocytic blast crisis of CML contain the mRNA in which bcr exon 2 is linked to ABL exon II. Finally, we identified, cloned, and characterized a BCR-related sequence that originated from mRNA.

The variable hematologic expression of the BCR-ABL genomic mutation and its possible determinants

The Philadelphia (Ph) chromosome usually results from the t(9;22), which causes the physical association of the BCR1 and ABL genes and their function as a single new gene. This precise genomic mutation probably has a significant role in the development of leukemia in humans, but that leukemia may take several forms: chronic myeloid leukemia (CML), acute myeloid leukemia, acute lymphocytic leukemia, and essential thrombocythemia; CML also transforms to a lymphoid or myeloid acute phase. Two models are considered with regard to determinants of this variable hematologic expression of BCR-ABL. The first is variation in the breakpoint site of BCR1. Two breakpoint sites, M-BCR and m-BCR, are known, and their occurrence shows a nonrandom association with the different forms of leukemia. The precise position of the breakpoint within M-BCR may also be important. The second model concerns the role of other genes in determining the leukemic form shown by BCR-ABL. Results are reviewed of a patient who entered blast crisis CML and whose leukemic clones involved ten genetic loci with known leukemic associations. Many of these were probably genetic variants that allowed leukemic proliferations following the initiation of blast crisis. The multiplicity of these genes may obscure the prime determinant of blast crisis, which is unknown at the present time.

Detection of rearrangement within the breakpoint cluster region of chromosome 22 in the diagnosis of chronic myeloid leukemia

Chronic myeloid leukemia (CML) is characterised by the presence of a Philadelphia (Ph) chromosome in approximately 95% of patients. Molecular analysis has shown that the Ph chromosome translocation breakpoints are clustered within 5.8 kb on chromosome 22 (breakpoint cluster region or bcr). This has facilitated the diagnosis of CML by nucleic acid hybridisation using probes specific for the bcr to detect DNA rearrangement in this region. Forty patients diagnosed with CML, including four with variant Ph chromosome translocations and three with normal karyotypes were analysed for rearrangement within the bcr. All except one patient with Ph negative CML had rearrangement within the bcr. In contrast, none of the patients diagnosed with other hematological disorders such as the myelodysplastic or myeloproliferative syndromes (16 patients), acute myeloid leukemia (AML) (six patients), acute lymphoblastic leukemia (ALL) (five patients), including Ph positive ALL (two patients), showed rearrangement within the bcr. Analysis for rearrangement within the bcr is useful in the diagnosis of CML, especially when cytogenetic analysis is unsuccessful or in patients with normal karyotypes or variant Ph chromosome translocations.

DNA rearrangement and restriction fragment length polymorphism within the first BCR intron in Philadelphia-positive acute leukemia

In some patients with Philadelphia (Ph)-chromosome positive acute lymphoblastic leukemias, breakpoints on chromosome 22 are reported to occur within the first BCR intron. To analyze the breakpoints in chromosome 22 of Ph-positive acute leukemia patients without rearrangement of the 5.8 kb bcr, we cloned the 3' part of the first BCR intron using a synthetic DNA probe. During the course of study, we mapped the region of the deletion/insertion of 1 kb that causes a restriction fragment length polymorphism (RFLP) and found a racial difference in the frequencies of the alleles giving rise to this RFLP. Analyses of the patients' samples indicated that breakpoints were located within the 8.5 kb EcoRl fragment of the first BCR intron in two of five Ph-positive acute leukemia patients. The data, together with the previous reports, indicate that breakpoints within this approximately 50 kb intron are widely scattered, in contrast to those confined within the 5.8 kb bcr in chronic myelogenous leukemias.

Alternative forms of the BCR-ABL oncogene have quantitatively different potencies for stimulation of immature lymphoid cells

The Philadelphia chromosome (t9:22;q34:q11) is found in more than 90% of patients with chronic myelogenous leukemia, in 10 to 20% of patients with acute lymphocytic leukemia, and in 1 to 2% of patients with acute myelogenous leukemia. Alternative chimeric oncogenes are formed by splicing different sets of BCR gene exons on chromosome 22 across the translocation breakpoint to a common set of ABL oncogene sequences on chromosome 9. This results in an 8.7-kilobase mRNA that encodes the P210 BCR-ABL gene product commonly found in patients with chronic myelogenous leukemia or a 7.0-kilobase mRNA that produces the P185 BCR-ABL gene product found in most Philadelphia chromosome-positive patients with acute lymphocytic leukemia. To compare the efficiency of growth stimulation by these two proteins, we derived cDNA clones for each with identical 5' and 3' untranslated regions and expressed them from retrovirus vectors. Matched stocks were compared for potency to transform immature B-lymphoid lineage precursors. The growth-stimulating effects of P185 for this cell type were found to be significantly greater than those of P210. Structural changes in BCR may regulate the effectiveness of the ABL tyrosine kinase function, as monitored by lymphocyte growth response. Changes in mitogenic potency may help to explain the more acute leukemic presentation usually associated with expression of the P185 BCR-ABL oncogene.

Direct and serial transplantation of Ph1-positive acute lymphoblastic leukemia into nude mice

A new Philadelphia chromosome (Ph1-positive) acute lymphoblastic leukemia (ALL) cell line was established in nude mice by direct and serial transplantation of peripheral blood leukemia cells from an adult patient. Although the patient's leukemia cells did not grow in vitro, they were successfully transplanted for 8 serial passages, giving rise to progressive growth of tumors with frequent involvement of lymph nodes, liver, spleen, bone marrow, and meninges. The tumor cells could also be passaged in an ascites form. This in vivo cell line, designated PALL-I, retained the Ph1 chromosome, t(9;22) (q34;q11), and pre-B-cell phenotype (SmIg-, CpIg-, CD10+, CD19+, OKIaI+, and CD38+), like the original leukemia cells. Molecular genetic analysis of PALL-I cells revealed neither bcr rearrangement nor 8.5-kb abI-related mRNA that is characteristically seen in Ph1-positive chronic myelogenous leukemia (CML). Thus, the PALL-I cell line is genetically distinct from CML. It may provide a useful model for an understanding of the cellular and molecular biology of Ph1-positive ALL without classical bcr rearrangement.

Unexpected heterogeneity of BCR-ABL fusion mRNA detected by polymerase chain reaction in Philadelphia chromosome-positive acute lymphoblastic leukemia

The Philadelphia (Ph1) chromosome results in a fusion of portions of the BCR gene from chromosome 22 and the ABL gene from chromosome 9, producing a chimeric BCR-ABL mRNA and protein. In lymphoblastic leukemias, there are two molecular subtypes of the Ph1 chromosome, one with a rearrangement of the breakpoint cluster region (bcr) of the BCR gene, producing the same 8.5-kilobase BCR-ABL fusion mRNA seen in chronic myelogenous leukemia (CML), and the other, without a bcr rearrangement, producing a 7.0-kilobase BCR-ABL fusion mRNA that is seen only in acute lymphoblastic leukemia (ALL). We studied the molecular subtype of the Ph1 chromosome in 11 cases of Ph1-positive ALL, including 2 with a previous diagnosis of CML, using a sensitive method to analyze the mRNA species based on the polymerase chain reaction (PCR). We observed unexpected heterogeneity in BCR-ABL mRNA in this population; in particular, 1 of 6 bcr-rearranged cases and 1 of 5 bcr-unrearranged cases contained none of the known fusion mRNA species, while 1 of the bcr-rearranged cases contained both. This latter case is particularly interesting because it suggests that the acquisition of an additional BCR-ABL fusion species may be a mechanism of disease progression. We conclude that the PCR gives additional information about the Ph1 chromosome gene products that cannot be obtained by genomic analysis, but that it cannot be used as the sole means of detection of this chromosomal abnormality in ALL because of the high incidence of false negative results.

Localization of preferential sites of rearrangement within the BCR gene in Philadelphia chromosome-positive acute lymphoblastic leukemia

The Philadelphia chromosome associated with acute lymphoblastic leukemia (ALL) has been linked to a hybrid BCR/ABL protein product that differs from that found in chronic myelogenous leukemia. This implies that the molecular structures of the two chromosomal translocations also differ. Localization of translocation breakpoints in Philadelphia chromosome-positive ALL has been impeded due to the only partial characterization of the BCR locus. We have isolated the entire 130-kilobase BCR genomic locus from a human cosmid library. A series of five single-copy genomic probes from the 70-kilobase first intron of BCR were used to localize rearrangements in 8 of 10 Philadelphia chromosome-positive ALLs. We have demonstrated that these breakpoints are all located at the 3' end of the intron around an unusual restriction fragment length polymorphism caused by deletion of a 1-kilobase fragment containing Alu family reiterated sequences. This clustering is unexpected in light of previous theories of rearrangement in Philadelphia chromosome-positive chronic myelogenous leukemia that would have predicted a random dispersion of breakpoints in the first intron in Philadelphia chromosome-positive ALL. The proximity of the translocation breakpoints to this constitutive deletion may indicate shared mechanisms of rearrangement or that such polymorphisms mark areas of the genome prone to recombination.

Mechanism of activation of the human trk oncogene

The human trk oncogene was generated by a genetic rearrangement that replaced the extracellular domain of the normal trk tyrosine kinase receptor by sequences coding for the 221 amino-terminal residues of a nonmuscle tropomyosin. Molecular dissection of a cDNA clone of the trk oncogene indicated that both the tropomyosin and tyrosine kinase domains were required for proper transforming activity. Replacement of nonmuscle tropomyosin sequences with those of other tropomyosin isoforms had no deleterious effect. However, when tropomyosin sequences were replaced with those of another cytoskeletal gene, such as beta-actin or beta-globin, transforming activity was completely abolished. These results illustrate the important role of tropomyosin sequences in endowing the trk kinase with transforming properties. Functionally unrelated subdomains of the tropomyosin molecule were equally efficient in activating the trk gene. Moreover, the transforming activity of the trk oncogene was not affected when its subcellular localization was drastically altered. Therefore, tropomyosin sequences are likely to contribute to the malignant activation of the trk oncogene not by facilitating its interaction with defined cytoskeletal structures as initially suspected, but by allowing its kinase domain to fold into a constitutively active configuration.

Alternative forms of the BCR-ABL oncogene have quantitatively different potencies for stimulation of immature lymphoid cells

The Philadelphia chromosome (t9:22;q34:q11) is found in more than 90% of patients with chronic myelogenous leukemia, in 10 to 20% of patients with acute lymphocytic leukemia, and in 1 to 2% of patients with acute myelogenous leukemia. Alternative chimeric oncogenes are formed by splicing different sets of BCR gene exons on chromosome 22 across the translocation breakpoint to a common set of ABL oncogene sequences on chromosome 9. This results in an 8.7-kilobase mRNA that encodes the P210 BCR-ABL gene product commonly found in patients with chronic myelogenous leukemia or a 7.0-kilobase mRNA that produces the P185 BCR-ABL gene product found in most Philadelphia chromosome-positive patients with acute lymphocytic leukemia. To compare the efficiency of growth stimulation by these two proteins, we derived cDNA clones for each with identical 5' and 3' untranslated regions and expressed them from retrovirus vectors. Matched stocks were compared for potency to transform immature B-lymphoid lineage precursors. The growth-stimulating effects of P185 for this cell type were found to be significantly greater than those of P210. Structural changes in BCR may regulate the effectiveness of the ABL tyrosine kinase function, as monitored by lymphocyte growth response. Changes in mitogenic potency may help to explain the more acute leukemic presentation usually associated with expression of the P185 BCR-ABL oncogene.

bcr rearrangement and C-abl gene expression in Ph1-positive hybrid acute leukemia with simultaneous proliferation of lymphoid and myeloid blasts

bcr gene rearrangement and c-abl gene expression were analyzed in a patient with Philadelphia chromosome (Ph1)-positive hybrid acute leukemia with simultaneous proliferation of lymphoid and myeloid blasts. These data were compared with those from a patient with chronic myelogenous leukemia (CML) in mixed crisis. The leukemic cells of both patients showed immuno-phenotypic profiles such as non-T, non-B common ALL with some MPO-positive leukemic cells and rearranged JH genes. On analysis of molecular events associated with the Ph1 chromosome, the leukemic cells of a patient with CML in mixed crisis showed bcr rearrangement and an 8.5-kb bcr-abl chimeric mRNA, but those of a patient with Ph1-positive hybrid acute leukemia showed no 8.5-kb bcr-abl mRNA, as previously reported in a number of Ph1-positive acute lymphoblastic leukemia (ALL) cases. These results revealed that the molecular event found in Ph1-positive ALL is not only restricted to lymphoid lineage but may play an important role in the proliferation of the myeloid lineage.