Cellular RNA homologous to the Abelson murine leukemia virus transforming gene: expression and relationship to the viral sequence

The Abl pathway bifurcates to balance Enabled and Rac signaling in axon patterning in Drosophila

The Abl tyrosine kinase signaling network controls cell migration, epithelial organization, axon patterning and other aspects of development. Although individual components are known, the relationships among them remain unresolved. We now use FRET measurements of pathway activity, analysis of protein localization and genetic epistasis to dissect the structure of this network in Drosophila We find that the adaptor protein Disabled stimulates Abl kinase activity. Abl suppresses the actin-regulatory factor Enabled, and we find that Abl also acts through the GEF Trio to stimulate the signaling activity of Rac GTPase: Abl gates the activity of the spectrin repeats of Trio, allowing them to relieve intramolecular repression of Trio GEF activity by the Trio N-terminal domain. Finally, we show that a key target of Abl signaling in axons is the WAVE complex that promotes the formation of branched actin networks. Thus, we show that Abl constitutes a bifurcating network, suppressing Ena activity in parallel with stimulation of WAVE. We suggest that the balancing of linear and branched actin networks by Abl is likely to be central to its regulation of axon patterning.

Oncogenic activation of c-ABL by mutation within its last exon

The c-ABL proto-oncogene is a predominantly nuclear localized tyrosine kinase. A random mutagenesis scheme was used to isolate c-ABL mutants whose expression produced a transformed phenotype in rodent fibroblast cells. An in-frame deletion within the central region of the last exon was identified in one ABL mutant. The mechanism of c-ABL oncogenic activation by mutation within the last exon differs both functionally and structurally from those of v-ABL and BCR/ABL. This class of ABL mutants shows increased tyrosine phosphorylation of cellular proteins in vivo but low levels of autophosphorylation. Last-exon ABL mutants are distinguished from v-ABL or BCR/ABL by their inability to transform primary bone marrow cells or support the growth of transformed pre-B cells. These findings define a new mechanism of oncogenic activation for the ABL kinase through mutations in the last exon which do not require amino-terminal deletions or mutations within the src homology regions.

Oncogenic activation of c-ABL by mutation within its last exon

The c-ABL proto-oncogene is a predominantly nuclear localized tyrosine kinase. A random mutagenesis scheme was used to isolate c-ABL mutants whose expression produced a transformed phenotype in rodent fibroblast cells. An in-frame deletion within the central region of the last exon was identified in one ABL mutant. The mechanism of c-ABL oncogenic activation by mutation within the last exon differs both functionally and structurally from those of v-ABL and BCR/ABL. This class of ABL mutants shows increased tyrosine phosphorylation of cellular proteins in vivo but low levels of autophosphorylation. Last-exon ABL mutants are distinguished from v-ABL or BCR/ABL by their inability to transform primary bone marrow cells or support the growth of transformed pre-B cells. These findings define a new mechanism of oncogenic activation for the ABL kinase through mutations in the last exon which do not require amino-terminal deletions or mutations within the src homology regions.

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.

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.

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.

Targeted gene disruption of the endogenous c-abl locus by homologous recombination with DNA encoding a selectable fusion protein

We have introduced a substitution mutation into the c-abl locus of murine embryonic stem cells by homologous recombination between exogenously added DNA and the endogenous gene. Model constructs were initially generated that consisted of a promoterless selectable neomycin resistance marker inserted into the v-abl gene of the complete Abelson murine leukemia virus genome, designed to be expressed either as a fusion protein or by translational restart. Tests of these viral genomes for transmission of v-abl and neo markers showed more stable coexpression in a protein fusion construct. The neo fusion was subcloned from this v-abl construct into a promoterless c-abl fragment, and the resulting DNA was used to transform embryonic stem cells. Direct screening of genomic DNAs showed that a high proportion of drug-resistant clones arose from homologous recombination into the endogenous c-abl locus.

Effect of 5-azacytidine on gene expression in marrow stromal cells

When exposed to 5-azacytidine, marrow stromal cells from active long-term marrow cultures and cell lines derived from simian virus 40-transformed stromal cells rapidly upregulated c-abl and interleukin-6 transcripts while downregulating the expression of collagen I, a major matrix protein. Similar effects occurred with interleukin-1 alpha and tumor necrosis factor alpha, although the time course was considerably prolonged.

Recombinant tumor necrosis factor alpha and interleukin 1 alpha increase expression of c-abl protooncogene mRNA in cultured human marrow stromal cells

Analysis of protooncogene RNA expression in marrow stromal cells from long-term marrow culture demonstrated high levels of c-abl 5-, 6-, and 7-kilobase (kb) RNA transcripts. In experiments on three independently derived simian virus 40-transformed marrow stromal cell lines, the expression of these c-abl transcripts was further increased in response to recombinant tumor necrosis factor alpha (1000 units/ml) and interleukin 1 alpha (10 units/ml). Although lymphocyte-conditioned medium predominantly up-regulated the 5-kb transcript, interleukin 1 alpha primarily affected the 6-kb transcript. The up-regulation of the 5-kb c-abl message correlated with up-regulation of the granulocyte/macrophage colony-stimulating factor transcript and down-regulation of procollagen I transcripts in transformed cells. These data suggest that c-abl plays roles in the regulation of extracellular matrix expression and in the regulation of hematopoietic growth factors by stromal cells.

Effect of 5-azacytidine on gene expression in marrow stromal cells

When exposed to 5-azacytidine, marrow stromal cells from active long-term marrow cultures and cell lines derived from simian virus 40-transformed stromal cells rapidly upregulated c-abl and interleukin-6 transcripts while downregulating the expression of collagen I, a major matrix protein. Similar effects occurred with interleukin-1 alpha and tumor necrosis factor alpha, although the time course was considerably prolonged.

Differential expression of type-specific c-abl mRNAs in mouse tissues and cell lines

The mammalian c-abl proto-oncogene produces mRNAs with 5' heterogeneity from two distinct promoters and the alternative splicing of variable 5' exons. By using quantitative RNase protection assays, the relative abundance of two major c-abl mRNAs, type I and type IV, in several mouse tissues and cell lines has been determined. Our results demonstrate that the level of type IV c-abl mRNA is rather constant, whereas that of the type I mRNA varies over a 10-fold range in different tissues and cell types. This finding has interesting implications for the function of the two c-abl proteins.

Differential expression of type-specific c-abl mRNAs in mouse tissues and cell lines

The mammalian c-abl proto-oncogene produces mRNAs with 5' heterogeneity from two distinct promoters and the alternative splicing of variable 5' exons. By using quantitative RNase protection assays, the relative abundance of two major c-abl mRNAs, type I and type IV, in several mouse tissues and cell lines has been determined. Our results demonstrate that the level of type IV c-abl mRNA is rather constant, whereas that of the type I mRNA varies over a 10-fold range in different tissues and cell types. This finding has interesting implications for the function of the two c-abl proteins.

Identification and sequence analysis of a new member of the mouse HSP70 gene family and characterization of its unique cellular and developmental pattern of expression in the male germ line

A unique member of the mouse HSP70 gene family has been isolated and characterized with respect to its DNA sequence organization and expression. The gene contains extensive similarity to a heat shock-inducible HSP70 gene within the coding region but diverges in both 3' and 5' nontranslated regions. The gene does not yield transcripts in response to heat shock in mouse L cells. Rather, the gene appears to be activated uniquely in the male germ line. Analysis of RNA from different developmental stages and from enriched populations of spermatogenic cells revealed that this gene is expressed during the prophase stage of meiosis. A transcript different in size from the major heat-inducible mouse transcripts is most abundant in meiotic prophase spermatocytes and decreases in abundance in postmeiotic stages of spermatogenesis. This pattern of expression is distinct from that observed for another member of this gene family, which was previously shown to be expressed abundantly in postmeiotic germ cells. These observations suggest that specific HSP70 gene family members play distinct roles in the differentiation of the germ cell lineage in mammals.

Identification and sequence analysis of a new member of the mouse HSP70 gene family and characterization of its unique cellular and developmental pattern of expression in the male germ line

A unique member of the mouse HSP70 gene family has been isolated and characterized with respect to its DNA sequence organization and expression. The gene contains extensive similarity to a heat shock-inducible HSP70 gene within the coding region but diverges in both 3' and 5' nontranslated regions. The gene does not yield transcripts in response to heat shock in mouse L cells. Rather, the gene appears to be activated uniquely in the male germ line. Analysis of RNA from different developmental stages and from enriched populations of spermatogenic cells revealed that this gene is expressed during the prophase stage of meiosis. A transcript different in size from the major heat-inducible mouse transcripts is most abundant in meiotic prophase spermatocytes and decreases in abundance in postmeiotic stages of spermatogenesis. This pattern of expression is distinct from that observed for another member of this gene family, which was previously shown to be expressed abundantly in postmeiotic germ cells. These observations suggest that specific HSP70 gene family members play distinct roles in the differentiation of the germ cell lineage in mammals.

DNA sequence, structure, and tyrosine kinase activity of the Drosophila melanogaster Abelson proto-oncogene homolog

We report our molecular characterization of the Drosophila melanogaster Abelson gene (abl), a gene in which recessive loss-of-function mutations result in lethality at the pupal stage of development. This essential gene consists of 10 exons extending over 26 kilobase pairs of genomic DNA. The DNA sequence encodes a protein of 1,520 amino acids with strong sequence similarity to the human c-abl proto-oncogene beginning in the type lb 5' exon and extending through the region essential for tyrosine kinase activity. When the tyrosine kinase homologous region was expressed in Escherichia coli, phosphorylation of proteins on tyrosine residues was observed with an antiphosphotyrosine antibody. These results show that the abl gene is highly conserved through evolution and encodes a functional tyrosine protein kinase required for Drosophila development.

Normal cellular and transformation-associated abl proteins share common sites for protein kinase C phosphorylation

Viral transduction and chromosomal translocations of the c-abl gene result in the synthesis of abl proteins with structurally altered amino termini. These altered forms of the abl protein, but not the c-abl proteins, are detectably phosphorylated on tyrosine in vivo. In contrast, all forms of the abl protein are phosphorylated on serine following in vivo labeling with Pi. Treatment of NIH-3T3 cells with protein kinase C activators resulted in a four- to eightfold increase in the phosphorylation of murine c-abl due to modification of two serines on the c-abl protein. Purified protein kinase C phosphorylated all abl proteins at the same two sites. Both sites are precisely conserved in murine and human abl proteins. The sites on the abl proteins were found near the carboxy terminus. In contrast, for the epidermal growth factor receptor (T. Hunter, N. Ling, and J. A. Cooper, Nature [London] 311:480-483, 1984) and pp60src (K. L. Gould, J. R. Woodgett, J. A. Cooper, J. E. Buss, D. Shalloway, and T. Hunter, Cell 42:849-857, 1985), the sites of protein kinase C phosphorylation are amino-terminal to the kinase domain. The abl carboxy-terminal region is not necessary for the tyrosine kinase activity or transformation potential of the viral abl protein and may represent a regulatory domain. Using an in vitro immune complex kinase assay, we were not able to correlate reproducible changes in c-abl activity with phosphorylation by protein kinase C. However, the high degree of conservation of the phosphorylation sites for protein kinase C between human and mouse abl proteins suggests an important functional role.

DNA sequence, structure, and tyrosine kinase activity of the Drosophila melanogaster Abelson proto-oncogene homolog

We report our molecular characterization of the Drosophila melanogaster Abelson gene (abl), a gene in which recessive loss-of-function mutations result in lethality at the pupal stage of development. This essential gene consists of 10 exons extending over 26 kilobase pairs of genomic DNA. The DNA sequence encodes a protein of 1,520 amino acids with strong sequence similarity to the human c-abl proto-oncogene beginning in the type lb 5' exon and extending through the region essential for tyrosine kinase activity. When the tyrosine kinase homologous region was expressed in Escherichia coli, phosphorylation of proteins on tyrosine residues was observed with an antiphosphotyrosine antibody. These results show that the abl gene is highly conserved through evolution and encodes a functional tyrosine protein kinase required for Drosophila development.

The first intron in the human c-abl gene is at least 200 kilobases long and is a target for translocations in chronic myelogenous leukemia

The c-abl protooncogene is unusual in two respects; it has multiple, widely space N-terminal coding exons transcribed by different promoters, and it is the target of the translocations that form the Philadelphia chromosome found in cells of chronic myelogenous leukemia patients. To understand the organization of the gene in normal and chronic myelogenous leukemia patient DNA we have mapped c-abl by pulsed field gradient gel electrophoresis. We find that one of the alternative 5' exons of the gene lies at least 200 kilobases upstream of the remaining c-abl exons, posing formidable transcription and splicing problems. The 5'-most c-abl exon includes an unusually long 1,276-base-pair segment that contains 15 ATG codons and multiple short open reading frames, upstream of the abl initiator codon. Its peculiar structure suggests that c-abl may be decapitated in most chronic myelogenous leukemia patients, and we demonstrate that this is the case in the chronic myelogenous leukemia cell line K562.

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.

Nucleotide sequence of testis-derived c-abl cDNAs: implications for testis-specific transcription and abl oncogene activation

The c-abl gene codes for a protein-tyrosine kinase and is expressed in most examined murine cell types as two distinct mRNA species of 5.5 kilobases (kb) and 6.5 kb. In mouse testis, an additional species of 4.0 kb is expressed in very high levels. To study the interrelationship between various c-abl transcripts and to compare their sequence with the v-abl transcript, we prepared c-abl-specific cDNA clones from mouse testis and determined the complete nucleotide sequence of the 4.0-kb cDNA that appears to be the reverse transcript of the testis-specific mRNA. In addition, we have determined the 3' sequence of an additional clone derived from the larger mRNA species that is expressed in somatic as well as germ-line cells. These cDNA sequences have been compared with the v-abl sequences to understand the mechanism of activation of this oncogene. The results demonstrate that (i) testis-specific c-abl mRNAs arise as a result of 3' truncation, and (ii) the v-abl gene has arisen from its cellular homologue as a result of an extensive deletional/mutational process.

Normal cellular and transformation-associated abl proteins share common sites for protein kinase C phosphorylation

Viral transduction and chromosomal translocations of the c-abl gene result in the synthesis of abl proteins with structurally altered amino termini. These altered forms of the abl protein, but not the c-abl proteins, are detectably phosphorylated on tyrosine in vivo. In contrast, all forms of the abl protein are phosphorylated on serine following in vivo labeling with Pi. Treatment of NIH-3T3 cells with protein kinase C activators resulted in a four- to eightfold increase in the phosphorylation of murine c-abl due to modification of two serines on the c-abl protein. Purified protein kinase C phosphorylated all abl proteins at the same two sites. Both sites are precisely conserved in murine and human abl proteins. The sites on the abl proteins were found near the carboxy terminus. In contrast, for the epidermal growth factor receptor (T. Hunter, N. Ling, and J. A. Cooper, Nature [London] 311:480-483, 1984) and pp60src (K. L. Gould, J. R. Woodgett, J. A. Cooper, J. E. Buss, D. Shalloway, and T. Hunter, Cell 42:849-857, 1985), the sites of protein kinase C phosphorylation are amino-terminal to the kinase domain. The abl carboxy-terminal region is not necessary for the tyrosine kinase activity or transformation potential of the viral abl protein and may represent a regulatory domain. Using an in vitro immune complex kinase assay, we were not able to correlate reproducible changes in c-abl activity with phosphorylation by protein kinase C. However, the high degree of conservation of the phosphorylation sites for protein kinase C between human and mouse abl proteins suggests an important functional role.

Abelson virus transformation of an interleukin 2-dependent antigen-specific T-cell line

Abelson murine leukemia virus (A-MuLV) carries the gene v-abl, one of a group of oncogenes with structural and functional (tyrosine kinase) homology to three growth factor receptors. Work in this and other laboratories has shown that A-MuLV infection can render myeloid and lymphoid cells independent of the growth factors interleukin 3 and granulocyte-macrophage colony-stimulating factor. We have now shown that v-abl can also relieve interleukin 2 (IL-2) dependence in T cells. We infected a cloned IL-2-dependent antigen-specific cell line. Transformed cells were generated which were factor independent and tumorigenic. The transformants each bore unique v-abl DNA inserts and expressed v-abl mRNA. No elevation of expression of either IL-2 or its receptor could be detected in these cells. Thus, A-MuLV can short-circuit the dependence of hematopoietic cells on IL-2, IL-3, and possibly granulocyte-macrophage colony-stimulating factor, none of whose receptors are known to be of the tyrosine kinase type.

The first intron in the human c-abl gene is at least 200 kilobases long and is a target for translocations in chronic myelogenous leukemia

The c-abl protooncogene is unusual in two respects; it has multiple, widely space N-terminal coding exons transcribed by different promoters, and it is the target of the translocations that form the Philadelphia chromosome found in cells of chronic myelogenous leukemia patients. To understand the organization of the gene in normal and chronic myelogenous leukemia patient DNA we have mapped c-abl by pulsed field gradient gel electrophoresis. We find that one of the alternative 5' exons of the gene lies at least 200 kilobases upstream of the remaining c-abl exons, posing formidable transcription and splicing problems. The 5'-most c-abl exon includes an unusually long 1,276-base-pair segment that contains 15 ATG codons and multiple short open reading frames, upstream of the abl initiator codon. Its peculiar structure suggests that c-abl may be decapitated in most chronic myelogenous leukemia patients, and we demonstrate that this is the case in the chronic myelogenous leukemia cell line K562.

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.

Abelson virus transformation of an interleukin 2-dependent antigen-specific T-cell line

Abelson murine leukemia virus (A-MuLV) carries the gene v-abl, one of a group of oncogenes with structural and functional (tyrosine kinase) homology to three growth factor receptors. Work in this and other laboratories has shown that A-MuLV infection can render myeloid and lymphoid cells independent of the growth factors interleukin 3 and granulocyte-macrophage colony-stimulating factor. We have now shown that v-abl can also relieve interleukin 2 (IL-2) dependence in T cells. We infected a cloned IL-2-dependent antigen-specific cell line. Transformed cells were generated which were factor independent and tumorigenic. The transformants each bore unique v-abl DNA inserts and expressed v-abl mRNA. No elevation of expression of either IL-2 or its receptor could be detected in these cells. Thus, A-MuLV can short-circuit the dependence of hematopoietic cells on IL-2, IL-3, and possibly granulocyte-macrophage colony-stimulating factor, none of whose receptors are known to be of the tyrosine kinase type.

Phosphotyrosine antibodies identify the p210c-abl tyrosine kinase and proteins phosphorylated on tyrosine in human chronic myelogenous leukemia cells

Antibodies against phosphotyrosine are a powerful tool with which to identify proteins phosphorylated on tyrosine residues, such as viral oncogene-encoded transforming proteins and their cellular protein substrates. Probed on human leukemia cell lines, phosphotyrosine antibodies recognized a 210,000-molecular-weight protein (p210) in K562 cells, a cell line derived from a Philadelphia (Ph)'-positive chronic myelogenous leukemia (CML), but recognized no protein in control Ph'-negative non-CML leukemia cells. The p210 protein was also recognized by antisera against v-abl-encoded polypeptides and displayed kinase activity, phosphorylating itself on tyrosine, in an immunocomplex kinase assay. These data are consistent with reported findings of the expression of a recombined bcr-abl gene in Ph'-positive CML cells, leading to the synthesis of an altered p210c-abl protein endowed with tyrosine kinase activity. Phosphotyrosine antibodies also detected the expression of the p210c-abl protein in fresh bone marrow cells harvested from CML patients in blast crisis. Besides the p210c-abl protein kinase, phosphotyrosine antibodies recognized other proteins with molecular weights of 110,000, 68,000, and 36,000 (p110, p68, and p36) in K562 cells. When [gamma-32P]ATP was added to nonionic detergent-extracted cells, these proteins became phosphorylated on tyrosine, as confirmed by phosphoamino acid analysis. A comparison with fibroblasts transformed by the v-abl, v-src, and v-fps oncogenes suggested the identity of the p36 protein with the common 36-kilodalton protein substrate of viral oncogene-encoded tyrosine kinases. Enhanced tyrosine phosphorylation of cellular proteins is thus a feature shared by cells transformed by v-abl and cells expressing a rearranged bcr-abl gene.

Molecular analysis of TCRB and ABL in a t(7;9)-containing cell line (SUP-T3) from a human T-cell leukemia

A translocation between chromosomes 7 and 9, t(7;9), has been described in cell lines derived from the malignant cells of children with acute T-cell lymphoblastic leukemia or lymphoma. Our cytogenetic analysis of one such cell line, SUP-T3, demonstrates that the breakpoints on chromosomes 7 and 9 lie within bands q36 and q34, respectively, corresponding to the location of the gene encoding the beta chain of the T-cell receptor, TCRB, and the gene homologous to the transforming gene of the Abelson murine leukemia virus, ABL. We investigated the role of these genes in the t(7;9). In situ chromosomal hybridization of TCRB and ABL probes to metaphase cells from SUP-T3 demonstrated that ABL is translocated from chromosome 9 to 7 and that all or part of TCRB is translocated from chromosome 7 to 9. Southern blot analysis revealed that both TCRB alleles were rearranged; however, it could not be determined whether the translocation breakpoint lies within this gene. Pulsed-field gel electrophoresis and Southern blot analysis were used to examine more than 500 kilobases of the ABL locus; we concluded that there are no rearrangements within 250 kb in either direction of the sequences homologous to v-abl. Additionally, no abnormal ABL protein was detected in an in vitro phosphorylation assay. These results indicate that, in SUP-T3, the breakpoint on chromosome 9 lies proximal to ABL and that the break results in no apparent alteration of the ABL protein. We therefore hypothesize that another gene on chromosome 9, at band q34, plays a role in this translocation. This study also demonstrates that pulsed-field gel electrophoresis is a powerful new tool for the analysis of human chromosomal translocations.

Breakpoints on chromosomes 9 and 22 in Philadelphia chromosome-positive chronic myelogenous leukemia (CML). Amplification of rearranged c-abl oncogenes in CML blast crisis

We surveyed 20 Philadelphia chromosome (Ph1) positive chronic myelogenous leukemia (CML) samples by Southern blot hybridization to determine the location of the breakpoints that occur on chromosomes 9 and 22 in the Ph1 translocation. Only 3 of 20 samples exhibited breakpoints on chromosome 9 within 18 kilobases (kb) of the v-abl homologous sequences. Mapping of these three chromosome 9 breakpoints indicates that each is at a separate location within this 18-kb region, indicating that there are no breakpoint "hot spots" in this area. In contrast, all 20 CML samples exhibited breaks on chromosome 22 within a 5.0-kb Bgl II fragment that lies within the previously described breakpoint cluster region (bcr). Several patients with CML blast crisis exhibiting multiple Ph1 chromosomes/metaphase exhibited amplified and rearranged c-abl-related fragments. These additional Ph1 chromosomes in blast crisis cells do not arise from a second, independent 9:22 translocation but rather result from a duplication of the preexisting Ph1 chromosome.

Phosphotyrosine antibodies identify the p210c-abl tyrosine kinase and proteins phosphorylated on tyrosine in human chronic myelogenous leukemia cells

Antibodies against phosphotyrosine are a powerful tool with which to identify proteins phosphorylated on tyrosine residues, such as viral oncogene-encoded transforming proteins and their cellular protein substrates. Probed on human leukemia cell lines, phosphotyrosine antibodies recognized a 210,000-molecular-weight protein (p210) in K562 cells, a cell line derived from a Philadelphia (Ph)'-positive chronic myelogenous leukemia (CML), but recognized no protein in control Ph'-negative non-CML leukemia cells. The p210 protein was also recognized by antisera against v-abl-encoded polypeptides and displayed kinase activity, phosphorylating itself on tyrosine, in an immunocomplex kinase assay. These data are consistent with reported findings of the expression of a recombined bcr-abl gene in Ph'-positive CML cells, leading to the synthesis of an altered p210c-abl protein endowed with tyrosine kinase activity. Phosphotyrosine antibodies also detected the expression of the p210c-abl protein in fresh bone marrow cells harvested from CML patients in blast crisis. Besides the p210c-abl protein kinase, phosphotyrosine antibodies recognized other proteins with molecular weights of 110,000, 68,000, and 36,000 (p110, p68, and p36) in K562 cells. When [gamma-32P]ATP was added to nonionic detergent-extracted cells, these proteins became phosphorylated on tyrosine, as confirmed by phosphoamino acid analysis. A comparison with fibroblasts transformed by the v-abl, v-src, and v-fps oncogenes suggested the identity of the p36 protein with the common 36-kilodalton protein substrate of viral oncogene-encoded tyrosine kinases. Enhanced tyrosine phosphorylation of cellular proteins is thus a feature shared by cells transformed by v-abl and cells expressing a rearranged bcr-abl gene.

Restriction fragment length polymorphism caused by a deletion within the human c-abl gene (ABL)

A restriction fragment length polymorphism at the human c-abl locus (ABL) has been detected in 67 unrelated individuals by agarose gel electrophoresis and Southern blot hybridization using 32P-labeled v-abl probes. This polymorphism is generated by the existence of two alleles, a and b, which are in Hardy-Weinberg equilibrium, with frequencies of 94.8% and 5.2%, respectively. The minor allele, b, is due to a deletion of about 500 base pairs in an intron located downstream of the codon for the phosphate-acceptor tyrosine residue of the c-abl gene product.

Isolation and characterization of Caenorhabditis elegans DNA sequences homologous to the v-abl oncogene

DNA sequences homologous to the v-abl oncogene were isolated from a Caenorhabditis elegans genomic library by their ability to hybridize with a v-src probe. The DNA sequence of 2465 nucleotides of one clone was determined. This region corresponds to the 5' protein kinase domain of v-abl plus approximately equal to 375 base pairs toward the 3' end. Four potential introns were identified. The homology between the deduced amino acid sequence of the C. elegans clone and that of the 1.2-kilobase-pair protein kinase region of v-abl is 62%. The tyrosine residue corresponding to the tyrosine that is phosphorylated in the v-src protein is conserved in the C. elegans sequence. When 95 amino acids around this tyrosine were compared with the corresponding sequences of Drosophila c-abl, v-abl, and v-src, the identities were 83%, 79%, and 56%, respectively. Hybridization of the cloned DNA with C. elegans poly(A)+ RNA revealed a major transcript of 4.4 kilobases.

Chromosomal localization and characterization of c-abl in the t(6;9) of acute nonlymphocytic leukemia

Acute nonlymphocytic leukemia associated with the chromosomal translocation t(6;9)(p23;q34) is an entity that is frequently associated with basophilia, which it shares with chronic myelogenous leukemia. The breakpoint on chromosome 9, q34, appears to be cytogenetically identical in both malignancies and is the site of the cellular oncogene c-abl. We investigated the role of c-abl in cells from two patients with the t(6;9) using in situ chromosomal hybridization, Southern hybridization, and in vitro phosphorylation. We showed that c-abl is not translocated from chromosome 9, resulting in a breakpoint that is on the 3' side of this gene. The t(6;9) translocation does not appear to result in the production of an aberrantly sized protein product or in the acquisition of in vitro tyrosine kinase activity. This is in direct contrast to the findings in chronic myelogenous leukemia, in which c-abl is translocated, leading to the production of a structurally altered c-abl protein with activated tyrosine kinase. Lastly, we demonstrated that the cells of one patient contain sequences from chromosome 9 inserted at the junction of a reciprocal translocation between chromosomes 4 and 10 on the 4q+ chromosome. This insertion, which is at least 100 kilobase pairs in length, represents a duplication and translocation of the protein coding region of c-abl.

Alternative processing and developmental control of the transcripts of the Drosophila abl oncogene homologue

Drosophila sequences homologous to the abl oncogene are located near the 5' end of a gene (Dash). The Dash gene is transcribed to give long RNAs (5-6 kb) and short RNAs (3.0 kb) that lack some of the internal exons of the gene including some of the sequences coding for the protein kinase domain. The gene is composed of at least five short exons and a long 3' exon. The 3' exon is processed in several alternative ways. It contains an intronic sequence which is spliced out in approximately 50% of the transcripts. S1 mapping shows the existence of five different 3' ends, presumed polyadenylation sites, differing by up to 1 kb. Three of these are maternal-specific while the other two are utilised during development. Dash RNA is most abundant in eggs and early embryos, becomes very rare during larval development and returns in a burst of activity in early pupae.

Haploid expression of a unique c-abl transcript in the mouse male germ line

RNA from immature mouse testes was shown to lack a low-molecular-weight c-abl transcript previously noted to be the predominant species in adult testes. The developmental pattern of appearance of this c-abl variant was determined by analyzing RNA obtained from purified populations of testicular cells in different stages of spermatogenesis. The appearance of the c-abl testicular variant was coincident with the entry of the germ cells into their haploid state and suggested that the regulated expression of this proto-oncogene may be important in the normal differentiation of the male germ line.

Haploid expression of a unique c-abl transcript in the mouse male germ line

RNA from immature mouse testes was shown to lack a low-molecular-weight c-abl transcript previously noted to be the predominant species in adult testes. The developmental pattern of appearance of this c-abl variant was determined by analyzing RNA obtained from purified populations of testicular cells in different stages of spermatogenesis. The appearance of the c-abl testicular variant was coincident with the entry of the germ cells into their haploid state and suggested that the regulated expression of this proto-oncogene may be important in the normal differentiation of the male germ line.

Developmental and molecular aspects of nephroblastomas induced by avian myeloblastosis-associated virus 2-O

Avian myeloblastosis-associated virus-induced nephroblastomas are tumors consisting mainly of mesenchymal and epithelial renal elements with variable degrees of differentiation. The spatial distribution of developmental stages reflects a gradient of differentiation from less differential structures in the periphery towards more differentiated structures in the center of the lobules formed in the nephroblastomas. These heterogenic tumors contain discrete virus-cell DNA junction fragments and are therefore clonal outgrowths of a single transformed cell. These findings support the hypothesis that a mesenchymal, nephrogenic cell residual in the postembryonic kidney is the origin of the tumor, which grows by proliferation and differentiation of this target cell. All the tumors expressed higher levels of viral genomic and env messages than nontransformed tissue from the same kidney. A screening of oncogene expression with 13 different oncogenes revealed enhanced myc levels. There was, however, no rearrangement of c-myc or of the other oncogenes detected with EcoRI-digested tumor DNAs. This suggests that there is no insertion of viral elements adjacent to a c-myc. The levels of myc expression in embryonic kidneys were as high as in the tumors. Therefore, the enhanced myc expression in nephroblastomas is a reflection of the embryonic status of the tumor rather than a newly acquired function. This finding, plus the similarity of development and morphology of nephroblastomas and embryonic kidneys, suggests that the tumors arise as a result of a deficiency in a function which turns the embryonic status off.

Protein stabilization explains the gag requirement for transformation of lymphoid cells by Abelson murine leukemia virus

The single protein encoded by Abelson murine leukemia virus is a fusion of sequence from the retroviral gag genes with the v-abl sequence. Deletion of most of the gag region from the transforming protein results in a virus capable of transforming fibroblasts but no longer capable of transforming lymphoid cells. Smaller deletions in gag reveal that p15 gag sequences are responsible for this effect, whereas deletion of p12 sequences had no effect on lymphoid transformation. In transformed fibroblasts, p15-deleted and normal proteins had similar activities and subcellular localization. When the p15-deleted genome was introduced into previously transformed lymphoid lines, its protein product exhibited a marked instability. The tyrosine-specific autophosphorylation activity per cell was less than 1/20th that of the nondeleted protein. Although pulse-Ia-beling showed that the p15-deleted protein was synthesized efficiently, immunoblotting demonstrated that its steady-state level was less than 1/10th that of the nondeleted Abelson protein. The specific instability of the p15-deleted protein in lymphoid cells explains the requirement of these sequences for lymphoid but not fibroblast transformation.

Expression of a proto-oncogene (proto-myb) in hemopoietic tissues of mice

This study addressed the possibility that proto-myb (also called c-myb), the cellular homolog of a retroviral transforming gene, plays a role in hemopoiesis, particularly during maturation of T cells. By gel blot hybridization, we confirmed previous reports that proto-myb transcripts are found at much higher levels in thymic lymphocytes and cells of the erythroid lineage than in other tissue sources. Using dot blot hybridizations, we demonstrated further that similar levels of proto-myb expression are found in thymic lymphocytes taken from young mice with active thymuses and from old mice whose thymuses have undergone involution and that the extent of proto-myb expression decreases at least 10-fold as T cells progress from immature cortical thymocytes to the mature, resting T cells taken from lymph nodes. These results suggest that the protein product of proto-myb functions during T-cell differentiation.

Human Cu/Zn superoxide dismutase gene: molecular characterization of its two mRNA species

Two cytoplasmic superoxide dismutase (SOD-1) mRNAs of about 0.7 and 0.9 kilobases (Kb.) were previously found in a variety of human cells. The two SOD-1 mRNAs are transcribed from the same gene and the major 0.7 Kb. species is approximately four times more abundant than the minor 0.9 Kb. mRNA. These two mRNAs differ in the length of their 3'-untranslated region and both have multiple 5'-ends. The longer transcript contains 222 additional nucleotides beyond the 3'-polyadenylated terminus of the short mRNA. S1 nuclease mapping and sequence analysis showed that these extra 222 nucleotides are specified by sequences contiguous to those shared by the two SOD-1 mRNAs. The 5'-termini of the two SOD-1 mRNAs were identified and mapped by both primer extension and S1 mapping. The majority of SOD-1 mRNA molecules (90-95%) have a 5'-start site located 23 base pairs (b.p.) downstream of the hexanucleotide -TATAAA-. The rest of the SOD-1 mRNA molecules have 5'-termini 30, 50 and 65 b.p. upstream from the major start region.

An 8-kilobase abl RNA transcript in chronic myelogenous leukemia

Chronic myelogenous leukemia (CML) is a clonal hematologic malignancy characterized by a reciprocal translocation between chromosomes 9 and 22 [t(9;22)] in greater than 90% of cases. This translocation results in a short chromosome 22, termed the Philadelphia (Ph1 or 22q-) chromosome. Recently, the cellular oncogenes abl and sis were mapped to human chromosomes 9 and 22, respectively. Moreover, abl was shown to be translocated from chromosome 9 to 22 and sis from chromosome 22 to 9 in CML patients with t(9;22). These findings raised the possibility that one or both of these oncogenes is activated and directly involved in the development of the disease. We analyzed expression of the abl and sis oncogenes in leukemic cells from CML patients with t(9;22). We found that sis is not expressed but that abl is transcribed into an 8-kilobase RNA. This abl RNA is also present in two leukemic cell lines (EM2 and K562), which were derived from CML patients and contain the t(9;22). This 8-kilobase RNA is not detected in normal cells, in other human leukemias without t(9;22), or in human cell lines that lack t(9;22). The consistent presence of this abl RNA transcript in CML with t(9;22) suggests that it is a consequence of abl translocation and that it plays a role in the development of this leukemia.

Transformation-associated proteins in murine B-cell lymphomas that are distinct from Abelson virus gene products

In an effort to identify cellular proteins that may be involved in the Abelson murine leukemia virus (A-MuLV) transformation process, we have isolated a hybridoma antibody (6C3) that detects a tumor-associated antigen in all A-MuLV-induced pre-B-cell lymphomas. The 6C3 antibody immunoprecipitates two molecules of Mr 160,000 and Mr 125,000 from metabolically labeled A-MuLV tumors. The two proteins recognized by the 6C3 antibody are distinct from the A-MuLV-transforming protein in that they lack viral gag determinants and are neither phosphoproteins nor protein kinases. The 6C3 proteins can be detected in all A-MuLV pre-B-cell lymphomas and some nonviral B lymphomas but are not detected on any other tumor or normal cell, including A-MuLV-transformed fibroblast lines. Thus, the 6C3 proteins may represent the products of novel cellular genes whose expression is induced, stabilized, or amplified in B-cell tumors of both viral and nonviral origin. Further evidence in support of this hypothesis is provided by the finding that 6C3 antigen expression correlates with autonomous cell growth and the transformed phenotype in both normal bone marrow cultures and those infected with A-MuLV.

Expression of a proto-oncogene (proto-myb) in hemopoietic tissues of mice

This study addressed the possibility that proto-myb (also called c-myb), the cellular homolog of a retroviral transforming gene, plays a role in hemopoiesis, particularly during maturation of T cells. By gel blot hybridization, we confirmed previous reports that proto-myb transcripts are found at much higher levels in thymic lymphocytes and cells of the erythroid lineage than in other tissue sources. Using dot blot hybridizations, we demonstrated further that similar levels of proto-myb expression are found in thymic lymphocytes taken from young mice with active thymuses and from old mice whose thymuses have undergone involution and that the extent of proto-myb expression decreases at least 10-fold as T cells progress from immature cortical thymocytes to the mature, resting T cells taken from lymph nodes. These results suggest that the protein product of proto-myb functions during T-cell differentiation.

Saccharomyces cerevisiae synthesizes proteins related to the p21 gene product of ras genes found in mammals

A family of normal vertebrate genes and oncogenes has been called the ras gene family. The name ras was assigned to this gene family based on the species of origin of the viral oncogenes of the rat-derived Harvey and Kirsten murine sarcoma viruses. There are now three known functional members of the ras gene family, and genes homologous to ras genes have been detected in the DNA of a wide variety of mammals and in Drosophila melanogaster. Prior experiments have detected proteins coded for by ras genes in a large number of normal cells, cell lines, and tumors. We report here the detection of ras-related proteins in D. melanogaster, a result predicted by the earlier detection of ras-related genes in the Drosophila genome. We also report for the first time the detection of ras-related proteins in a single-cell eucaryocyte, Saccharomyces cerevisiae. These proteins, approximately 30K in size, are recognized by both a monoclonal antibody which binds to the p21 coded for by mammalian ras genes and a polyclonal rat serum made by transplanting a v-Ha-ras-induced tumor in Osborne-Mendel rats. The p21 of v-Ha-ras and the 30K proteins from S. cerevisiae share methionine-labeled peptides as detected by two-dimensional tryptic peptide maps. The results indicate that S. cerevisiae synthesizes ras-related proteins. A genetic analysis of the function of these proteins for yeast cells may now be possible.

Saccharomyces cerevisiae synthesizes proteins related to the p21 gene product of ras genes found in mammals

A family of normal vertebrate genes and oncogenes has been called the ras gene family. The name ras was assigned to this gene family based on the species of origin of the viral oncogenes of the rat-derived Harvey and Kirsten murine sarcoma viruses. There are now three known functional members of the ras gene family, and genes homologous to ras genes have been detected in the DNA of a wide variety of mammals and in Drosophila melanogaster. Prior experiments have detected proteins coded for by ras genes in a large number of normal cells, cell lines, and tumors. We report here the detection of ras-related proteins in D. melanogaster, a result predicted by the earlier detection of ras-related genes in the Drosophila genome. We also report for the first time the detection of ras-related proteins in a single-cell eucaryocyte, Saccharomyces cerevisiae. These proteins, approximately 30K in size, are recognized by both a monoclonal antibody which binds to the p21 coded for by mammalian ras genes and a polyclonal rat serum made by transplanting a v-Ha-ras-induced tumor in Osborne-Mendel rats. The p21 of v-Ha-ras and the 30K proteins from S. cerevisiae share methionine-labeled peptides as detected by two-dimensional tryptic peptide maps. The results indicate that S. cerevisiae synthesizes ras-related proteins. A genetic analysis of the function of these proteins for yeast cells may now be possible.