Monoclonal antibodies specific for v-abl- and c-abl-encoded molecules

Structural and functional dissection of the DH and PH domains of oncogenic Bcr-Abl tyrosine kinase

The two isoforms of the Bcr-Abl tyrosine kinase, p210 and p190, are associated with different leukemias and have a dramatically different signaling network, despite similar kinase activity. To provide a molecular rationale for these observations, we study the Dbl-homology (DH) and Pleckstrin-homology (PH) domains of Bcr-Abl p210, which constitute the only structural differences to p190. Here we report high-resolution structures of the DH and PH domains and characterize conformations of the DH-PH unit in solution. Our structural and functional analyses show no evidence that the DH domain acts as a guanine nucleotide exchange factor, whereas the PH domain binds to various phosphatidylinositol-phosphates. PH-domain mutants alter subcellular localization and result in decreased interactions with p210-selective interaction partners. Hence, the PH domain, but not the DH domain, plays an important role in the formation of the differential p210 and p190 Bcr-Abl signaling networks.

Differential signaling networks of Bcr-Abl p210 and p190 kinases in leukemia cells defined by functional proteomics

The two major isoforms of the oncogenic Bcr–Abl tyrosine kinase, p210 and p190, are expressed upon the Philadelphia chromosome translocation. p210 is the hallmark of chronic myelogenous leukemia, whereas p190 occurs in the majority of B-cell acute lymphoblastic leukemia. Differences in protein interactions and activated signaling pathways that may be associated with the different diseases driven by p210 and p190 are unknown. We have performed a quantitative comparative proteomics study of p210 and p190. Strong differences in the interactome and tyrosine phosphoproteome were found and validated. Whereas the AP2 adaptor complex that regulates clathrin-mediated endocytosis interacts preferentially with p190, the phosphatase Sts1 is enriched with p210. Stronger activation of the Stat5 transcription factor and the Erk1/2 kinases is observed with p210, whereas Lyn kinase is activated by p190. Our findings provide a more coherent understanding of Bcr–Abl signaling, mechanisms of leukemic transformation, resulting disease pathobiology and responses to kinase inhibitors.

Charting the molecular network of the drug target Bcr-Abl

The tyrosine kinase Bcr-Abl causes chronic myeloid leukemia and is the cognate target of tyrosine kinase inhibitors like imatinib. We have charted the protein-protein interaction network of Bcr-Abl by a 2-pronged approach. Using a monoclonal antibody we have first purified endogenous Bcr-Abl protein complexes from the CML K562 cell line and characterized the set of most tightly-associated interactors by MS. Nine interactors were subsequently subjected to tandem affinity purifications/MS analysis to obtain a molecular interaction network of some hundred cellular proteins. The resulting network revealed a high degree of interconnection of 7 "core" components around Bcr-Abl (Grb2, Shc1, Crk-I, c-Cbl, p85, Sts-1, and SHIP-2), and their links to different signaling pathways. Quantitative proteomics analysis showed that tyrosine kinase inhibitors lead to a disruption of this network. Certain components still appear to interact with Bcr-Abl in a phosphotyrosine-independent manner. We propose that Bcr-Abl and other drug targets, rather than being considered as single polypeptides, can be considered as complex protein assemblies that remodel upon drug action.

Mutations affecting the MA portion of the v-Abl protein reveal a conserved role of Gag in Abelson murine leukemia virus (MLV) and Moloney MLV

Abelson murine leukemia virus (Ab-MLV) arose from a recombination between gag sequences in Moloney MLV (Mo-MLV) and the c-abl proto-oncogene. The v-Abl oncoprotein encoded by Ab-MLV contains MA, p12, and a portion of CA sequences derived from the gag gene of Mo-MLV. Previous studies indicated that alteration of MA sequences affects the biology of Mo-MLV and Ab-MLV. To understand the role of these sequences in Ab-MLV transformation more fully, alanine substitution mutants that affect Mo-MLV replication were examined in the context of Ab-MLV. Mutations affecting Mo-MLV replication decreased transformation, while alanine mutations in residues dispensable for Mo-MLV replication did not. The altered v-Abl proteins displayed aberrant subcellular localization that correlated to transformation defects. Immunofluorescent analyses suggested that aberrant trafficking of the altered proteins and improper interaction with components of the cytoskeleton were involved in the phenotype. Similar defects in localization were observed when the Gag moiety containing these mutations was expressed in the absence of abl-derived sequences. These results indicate that MA sequences within the Gag moiety of the v-Abl protein contribute to proper localization by playing a dominant role in trafficking of the v-Abl molecule.

Gag influences transformation by Abelson murine leukemia virus and suppresses nuclear localization of the v-Abl protein

Like the v-Onc proteins encoded by many transforming retroviruses, the v-Abl protein is expressed as a Gag-Onc fusion. Although the Gag-derived myristoylation signal targets the v-Abl protein to the plasma membrane, the protein contains the entire MA and p12 sequences and a small number of CA-derived residues. To understand the role of Gag sequences in transformation, mutants lacking portions of these sequences were examined for the effects of these deletions on v-Abl function and localization. Deletion of the N-terminal third of p12 or all of p12 enhanced the transformation of both pre-B cells and NIH 3T3 cells. In contrast, deletions in MA or a deletion removing all of Gag except the first 34 amino acids important for myristoylation highly compromised the ability to transform either cell type. Although all of the mutant proteins retained kinase activity, those defective in transformation were reduced in their ability to activate Erk, suggesting a role for Gag sequences in v-Abl signaling. Immunofluorescence analysis revealed that a v-Abl protein retaining only the first 34 amino acids of Gag localized to the nucleus. These data indicate that Gag sequences are important for normal v-Abl signaling and that they suppress nuclear localization of the molecule.

Disruption of the Shc/Grb2 complex during abelson virus transformation affects proliferation, but not apoptosis

The v-Abl protein tyrosine kinase encoded by Abelson murine leukemia virus (Ab-MLV) induces pre-B-cell transformation. Signals emanating from the SH2 domain of the protein are required for transformation, and several proteins bind this region of v-Abl. One such protein is the adaptor molecule Shc, a protein that complexes with Grb2/Sos and facilitates Ras activation, an event associated with Ab-MLV transformation. To test the role this interaction plays in growth and survival of infected pre-B cells, dominant-negative (DN) Shc proteins were coexpressed with v-Abl and transformation was examined. Expression of DN Shc reduced Ab-MLV pre-B-cell transformation and decreased the ability of v-Abl to stimulate Ras activation and Erk phosphorylation in a Raf-dependent but Rac-independent fashion. Further analysis revealed that Shc is required for v-Abl-mediated Raf tyrosine 340 and 341 phosphorylation, an event associated with Erk phosphorylation. In contrast to effects on proliferation, survival of the cells and activation of Akt were not affected by expression of DN Shc. Together, these data reveal that v-Abl-Shc interactions are a critical part of the growth stimulatory signals delivered during transformation but that they do not affect antiapoptotic pathways. Furthermore, these data highlight a novel role for Shc in signaling from v-Abl to Raf.

p16(Ink4a) interferes with Abelson virus transformation by enhancing apoptosis

Pre-B-cell transformation by Abelson virus (Ab-MLV) is a multistep process in which primary transformants are stimulated to proliferate but subsequently undergo crisis, a period of erratic growth marked by high levels of apoptosis. Inactivation of the p53 tumor suppressor pathway is an important step in this process and can be accomplished by mutation of p53 or down-modulation of p19(Arf), a p53 regulatory protein. Consistent with these data, pre-B cells from either p53 or Ink4a/Arf null mice bypass crisis. However, the Ink4a/Arf locus encodes both p19(Arf) and a second tumor suppressor, p16(Ink4a), that blocks cell cycle progression by inhibiting Cdk4/6. To determine if p16(Ink4a) plays a role in Ab-MLV transformation, primary transformants derived from Arf(-/-) and p16(Ink4a(-/-)) mice were compared. A fraction of those derived from Arf(-/-) animals underwent crisis, and even though all p16(Ink4a(-/-)) primary transformants experienced crisis, these cells became established more readily than cells derived from +/+ mice. Analyses of Ink4a/Arf(-/-) cells infected with a virus that expresses both v-Abl and p16(Ink4a) revealed that p16(Ink4a) expression does not alter cell cycle profiles but does increase the level of apoptosis in primary transformants. These results indicate that both products of the Ink4a/Arf locus influence Ab-MLV transformation and reveal that in addition to its well-recognized effects on the cell cycle, p16(Ink4a) can suppress transformation by inducing apoptosis.

Cell context-specific effects of the BCR-ABL oncogene monitored in hematopoietic progenitors

Acute BCR-ABL expression during in vitro hematopoietic development of embryonic stem (ES) cells causes expansion of multipotent and myeloid progenitors with a concomitant reduction in differentiation toward erythroblasts. Progenitor cell expansion is due to a rapid, cell autonomous, suppression of programmed cell death with an increase in expression of the antiapoptotic molecule BCL-X(L). Other antiapoptotic effectors, including AKT, STAT5, and BCL-2 are not up-regulated by BCR-ABL in this system. In addition, the proapoptotic p38 mitogen-activated protein kinase (MAPK) pathway is suppressed by BCR-ABL expression in ES-derived hematopoietic progenitors. Inhibition of p38 MAPK by the small molecule inhibitor SB203580 expanded ES-derived hematopoietic progenitors by an antiapoptotic mechanism and is sufficient to expand ES-derived hematopoietic progenitors to levels approaching 80% of that seen following BCR-ABL expression. In the cellular context of ES-derived hematopoietic progenitors, BCR-ABL expression expands cells by suppressing programmed cell death with a set of antiapoptotic pathways distinct from those previously reported in continuous cell line studies.

Temperature-sensitive transformation by an Abelson virus mutant encoding an altered SH2 domain

Abelson murine leukemia virus (Ab-MLV) encodes the v-Abl protein tyrosine kinase and induces transformation of immortalized fibroblast lines and pre-B cells. Temperature-sensitive mutations affecting the kinase domain of the protein have demonstrated that the kinase activity is absolutely required for transformation. Despite this requirement, mutations affecting other regions of v-Abl modulate transformation activity. The SH2 domain and the highly conserved FLVRES motif within it form a phosphotyrosine-binding pocket that is required for interactions between the kinase and cellular substrates. To understand the impact of SH2 alterations on Ab-MLV-mediated transformation, we studied the Ab-MLV mutant P120/R273K. This mutant encodes a v-Abl protein in which the beta B5 arginine at the base of the phosphotyrosine-binding pocket has been replaced by a lysine. Unexpectedly, infection of NIH 3T3 or pre-B cells with P120/R273K revealed a temperature-dependent transformation phenotype. At 34 degrees C, P120/R273K transformed about 10-fold fewer cells than wild-type virus of equivalent titer; at 39.5 degrees C, 300-fold fewer NIH 3T3 cells were transformed and pre-B cells were refractory to transformation. Temperature-dependent transformation was accompanied by decreased phosphorylation of Shc, a protein that interacts with the v-Abl SH2 and links the protein to Ras, and decreased induction of c-Myc expression. These data suggest that alteration of the FLVRES pocket affects the ability of v-Abl to interact with at least some of its substrates in a temperature-dependent fashion and identify a novel type of temperature-sensitive Abelson virus.

Localization and phosphorylation of Abl-interactor proteins, Abi-1 and Abi-2, in the developing nervous system

Abl-interactor (Abi) proteins are targets of Abl-family nonreceptor tyrosine kinases and are required for Rac-dependent cytoskeletal reorganization in response to growth factor stimulation. We asked if the expression, phosphorylation, and cellular localization of Abi-1 and Abi-2 supports a role for these proteins in Abl signaling in the developing and adult mouse nervous system. In mid- to late-gestation embryos, abi-2 message is elevated in the central and peripheral nervous systems (CNS and PNS). Abi-1 mRNA is present, but not enhanced, in the CNS, and is not observed in PNS structures. Abi proteins from brain lysates undergo changes in apparent molecular weight and phosphorylation with increasing age. In the postnatal brain, abi-1 and abi-2 are expressed most prominently in cortical layers populated by projection neurons. In cultured neurons, Abi-1 and Abi-2 are concentrated in puncta throughout the cell body and processes. Both Abi and Abl proteins are present in synaptosomes and growth cone particles. Therefore, the Abi adaptors exhibit proper expression patterns and subcellular localization to participate in Abl kinase signaling in the nervous system.

c-abl is involved in the association of p53 and trk A

The p53 tumour suppressor phosphoprotein associates with proteins involved in DNA replication, transcription, cell cycle machinery and regulation of its own expression. Recently it has been shown that p53 can also bind to trk A tyrosine kinase which is the receptor for nerve growth factor (NGF). This study demonstrates that p53 appears to associate with trk A via c-abl. Endogenous c-abl was detected when the trk A and p53 complex was immunoprecipitated from lysates of NGF stimulated NIH3T3 cells expressing trk A or NIH3T3 cells expressing trk A and a temperature sensitive p53 (val 135). Endogenous c-abl and trk A association was observed in NGF stimulated p53 negative fibroblasts transfected with trk A alone; suggesting that c-abl can independently bind to trk A in the absence of p53. Interestingly, association between endogenous p53 and trk A was not detected in NGF stimulated abl negative fibroblasts transfected with trk A or when these cells were exposed to gamma radiation. This result suggests that p53 preferentially binds to trk A in the presence of c-abl and that p53 and trk A do not appear to associate directly even if p53 is activated and its levels increased by gamma radiation. Overall, these data suggest that c-abl is possibly acting as an adaptor or bridge between p53 and trk A. Oncogene (2000).

Regulated expression of P210 Bcr-Abl during embryonic stem cell differentiation stimulates multipotential progenitor expansion and myeloid cell fate

P210 Bcr-Abl is an activated tyrosine kinase oncogene encoded by the Philadelphia chromosome associated with human chronic myelogenous leukemia (CML). The disease represents a clonal disorder arising in the pluripotent hematopoietic stem cell. During the chronic phase, patients present with a dramatic expansion of myeloid cells and a mild anemia. Retroviral gene transfer and transgenic expression in rodents have demonstrated the ability of Bcr-Abl to induce various types of leukemia. However, study of human CML or rodent models has not determined the direct and immediate effects of Bcr-Abl on hematopoietic cells from those requiring secondary genetic or epigenetic changes selected during the pathogenic process. We utilized tetracycline-regulated expression of Bcr-Abl from a promoter engineered for robust expression in primitive stem cells through multilineage blood cell development in combination with the in vitro differentiation of embryonal stem cells into hematopoietic elements. Our results demonstrate that Bcr-Abl expression alone is sufficient to increase the number of multipotent and myeloid lineage committed progenitors in a dose-dependent manner while suppressing the development of committed erythroid progenitors. These effects are reversible upon extinguishing Bcr-Abl expression. These findings are consistent with Bcr-Abl being the sole genetic change needed for the establishment of the chronic phase of CML and provide a powerful system for the analysis of any genetic change that alters cell growth and lineage choices of the hematopoietic stem cell.

Expression of BCR - ABL in M1 myeloid leukemia cells induces differentiation without arresting proliferation

The mechanism leading to the expanding population of maturing myeloid cells which characterises chronic myeloid leukemia (CML) remains obscure. Because of its ability to mimic the proliferative and cell survival functions of hematopoietic growth factors, we hypothesized that the oncogene activated in CML, BCR-ABL, might also influence differentiation. To test this hypothesis, we examined the effects of expressing BCR-ABL on the myeloid differentiation of murine M1 leukemic cells, which cease dividing and differentiate into macrophages in the presence of the cytokines leukemia inhibitory factor (LIF) or interleukin (IL)-6. We found that BCR-ABL induced macrophage differentiation in M1 cells, accompanied by increased expression of macrophage cell surface markers and the acquisition of phagocytic ability. interestingly, clones of M1 cells which expressed BCR-ABL remained in cell cycle and were refractory to the growth inhibition and apoptosis induced by IL-6 or LIF in parental M1 cells. These cells also expressed inappropriately high levels of c-MYC mRNA for their degree of differentiation, which may have been important in maintaining cellular proliferation. These data suggest that BCR-ABL can stimulate both differentiation and proliferation and that these characteristics may contribute to the phenotype observed in CML.

c-Abl proto-oncoprotein is expressed and tyrosine phosphorylated in human sperm cell

The presence and possible role of c-Abl proto-oncoprotein was investigated in human sperm cell. The c-Abl monoclonal antibody (mAb), against the protein tyrosine kinase domain of v-Abl protein, reacted specifically with the acrosomal region of methanol-fixed capacitated and non-capacitated human sperm cell in the indirect immunofluorescence technique. The c-Abl mAb predominantly recognized two protein bands of 145 kD and 95 kD in detergent-solubilized (Triton X-100 and NP-40) sperm and testes preparations in the Western blot procedure. The 95 kD protein band reacted stronger than the 145 kD band and was the only band detected in the lithium diiodosalicylate (LIS)-solubilized sperm preparation, and even in the Triton X-100/NP-40 extracts of sperm of some men. In the in vitro kinase assay using the Triton X-100-solubilized capacitated sperm preparation, the 95 kD protein was autophosphorylated at the tyrosine residues, which was inhibited in the presence of c-Abl mAb. The tyrosine phosphorylation of sperm proteins, especially of the 95 kD protein, has been shown to have a vital role in human sperm function, namely, the sperm capacitation/acrosomal exocytosis and binding to zona pellucida of oocyte. These findings suggest that the c-Abl or c-Abl-like proteins are present in mature sperm cells that are tyrosine autophosphorylated and may have a role in human sperm cell function.

The murine AIDS virus Gag precursor protein binds to the SH3 domain of c-Abl

The Pr60gag protein of the murine AIDS (MAIDS) defective virus promotes the proliferation of the infected target B cells and is responsible for inducing a severe immunodeficiency disease. Using the yeast two-hybrid system, we identified the SH3 domain of c-Abl as interacting with the proline-rich p12 domain of Pr60gag. The two proteins were shown to associate in vitro and in vivo in MAIDS virus-infected B cells. Overexpression of Pr60(gag) in these cells led to a detectable increase of the levels of c-Abl protein and to its translocation at the membrane. These results suggest that this viral protein serves as a docking site for signaling molecules and that c-Abl may be involved in the proliferation of infected B cells.

P210 and P190(BCR/ABL) induce the tyrosine phosphorylation and DNA binding activity of multiple specific STAT family members

The products of the Philadelphia chromosome translocation, P210 and P190(BCR/ABL), are cytoplasmic protein tyrosine kinases that share the ability to transform hematopoietic cytokine-dependent cell lines to cytokine independence but differ in the spectrum of leukemia induced in vivo. We have analyzed the Janus kinase (JAK) and signal transducer and activator of transcription (STAT) pathways in hematopoietic cells transformed by Bcr/Abl. STAT5 and, to a lesser extent, STATs 1 and 3 were constitutively activated by tyrosine phosphorylation and induction of DNA binding activity in both P210 and P190(BCR/ABL)-transformed cells, but P190 differed in that it also prominently activated STAT6. There was low level tyrosine phosphorylation of JAKs 1, 2, and 3 in Bcr/Abl-transformed cells, but no detectable complex formation with Bcr/Abl, and activation of STAT5 by P210 was not blocked by two different dominant-negative JAK mutants. These results suggest that P210 and P190(BCR/ABL) directly activate specific STAT family members and may help explain their overlapping yet distinct roles in leukemogenesis.

In vivo association of v-Abl with Shc mediated by a non-phosphotyrosine-dependent SH2 interaction

A necessary downstream element of Abelson murine leukemia virus (Ab-MLV)-mediated transformation is Ras, which can be activated by the phosphotyrosine-dependent association of Shc with the Grb2-mSos complex. Here we show that Shc is tyrosine-phosphorylated and associates with Grb2 in v-Abl-transformed cells, whereas Shc in NIH3T3 cells is phosphorylated solely on serine and is not Grb2-associated. In addition, Shc coprecipitates with P120 v-Abl and P70 v-Abl, which lacks the carboxyl terminus. Surprisingly, a kinase-defective mutant of P120 also binds Shc, demonstrating that Shc/v-Abl association is a phosphotyrosine-independent interaction. Glutathione S-transferase fusion proteins were used to map the interacting domains and showed that Shc from both NIH3T3 and v-Abl-transformed cells binds to the Abl SH2 domain and that P120 v-Abl binds to a region in the amino terminus of Shc. Consistent with these data, a v-Abl mutant encoding only the Gag and SH2 regions was able to bind Shc in vivo. The unique non-phosphotyrosine-mediated binding of Shc may allow direct tyrosine phosphorylation of Shc by v-Abl and subsequent activation of the Ras pathway through assembly of a signaling complex with Grb2-mSos.

Ras complements the carboxyl terminus of v-Abl protein in lymphoid transformation

Abelson murine leukemia virus (Ab-MLV) mutants expressing v-Abl proteins lacking the carboxyl terminus are compromised in the ability to transform lymphoid but not NIH 3T3 cells. This feature correlates with the presence of low levels of phosphotyrosine in lymphoid cells infected with carboxyl-terminal truncation mutants. In contrast, high levels of phosphotyrosine are observed in NIH 3T3 cells infected with wild-type and mutant Ab-MLV. Two downstream targets affected in lymphoid transformants are the GTPase-activating protein and GTPase-activating protein-associated protein p62, molecules which are heavily tyrosine phosphorylated in lymphoid cells transformed by wild-type Ab-MLV but not carboxyl-terminal truncation mutants of Ab-MLV. This difference suggested that signaling mediated via the Ras pathway may be compromised in lymphoid cells expressing the carboxyl-terminal truncation mutants. Consistent with this idea, expression of v-Ha-ras complemented these mutants in primary bone marrow transformation assays and increased transformation frequencies obtained with the Ab-MLV mutants 8- to 20-fold. These data suggest that a biologically important link exists between the carboxyl terminus of v-Abl protein and the Ras pathway. Signals transmitted via this connection may enhance those mediated via other regions of the v-Abl protein and facilitate transformation of primary, nonimmortalized cells such as pre-B lymphocytes.

Tissue-regulated differentiation and maturation of a v-abl-immortalized mast cell-committed progenitor

An immature v-abl-transformed mast cell line (V3-MC) was derived from a mouse that developed systemic mastocytosis after transplantation of v-abl-infected bone marrow cells. V3-MCs injected intravenously into adult BALB/c mice infiltrated the liver, spleen, and intestine by day 6 and underwent progressive differentiation and maturation, eventually resembling indigenous mast cells. In terms of their protease content, the V3-MCs that localized in the liver and spleen differed from those in the intestine, and both differed from the cultured V3-MCs. The acquired expression of certain proteases and the loss of expression of other proteases in these tissue V3-MCs defines particular phenotypes and indicates that the differentiation and maturation of mast cell-committed progenitor cells are primarily regulated by factors in the different tissue microenvironments.

Protein phosphorylation pattern and role of products of c-erbB-1 and c-abl proto-oncogenes in murine preimplantation embryonic development

PROBLEM

To investigate the protein phosphorylation pattern and role of products of c-erbB-1 and c-abl proto-oncogenes with known tyrosine kinase activity in preimplantation embryonic development in mice.

METHOD

The protein phosphorylation pattern was studied by in vitro 32P metabolic labeling of murine ova/embryos as well as by in vitro kinase assay performed directly on various ova/embryos extracts. The role of products of c-erbB-1 (170 kDa, receptor for epidermal growth factor [EGF]) and c-abl proto-oncogenes (150 kDa) was examined by in vitro culturing murine embryos in the presence of monoclonal antibodies to respective protein products and by co-culturing with EGF, the ligand for EGF receptor (EGF-R).

RESULTS

In vitro metabolic labeling of murine ova/embryos showed 32P incorporation into at least two protein bands of murine ova (M(r) 81 and 36 kDa), six protein bands of two-cell (M(r) 81, 36; and 97, 52, 22 and 19 kDa, respectively), six protein bands of morula (M(r) 81, 36; 97, 22, and 19; and 33 kDa, respectively), and eight protein bands of blastocyst (81, 36; 97, 22, 19; and 115, 58, and 15 kDa, respectively), stage embryos; there were some specific bands in each stage. Prolonged labeling from 2 to 4 h not only resulted in a relative increase in 32P incorporation into these proteins but also revealed additional bands in morula (M(r) 133 and 115 kD) and blastocyst (M(r) 49, 33, and 31 kD) stage embryos. In vitro kinase assays performed directly on various ova/embryos extracts revealed at least three phosphoproteins (M(r) 58, 36 and 33, respectively) that were common to ova, two-cell, morula, and early/late blastocyst stage embryos. Additionally, three protein bands each in murine ova and two-cell embryos (M(r) 108, 81, 73 kDa, respectively), and four protein bands of late blastocyst (M(r) 108, 73; 133 and 18 kDa, respectively) stage embryos were also revealed. Culture of two-cell embryos in the presence of EGF, the ligand for EGF-receptor, resulted in a concentration dependent increase (P < .001) in the number of cells per blastocyst. Monoclonal antibody to c-erbB-1 170 kDa protein (receptor for EGF) did not affect development of in vitro cultured murine embryos from two-cell to morula, but significantly (P < .001) inhibited the in vitro development of morula to late blastocyst stage. Monoclonal antibody to c-abl protein inhibited the development of murine embryos from two-cell to morula (P < .017), as well as, from morula to late blastocyst stage (P < .002 to .01).

CONCLUSIONS

These results suggest that the stage-specific protein phosphorylation pattern and specific products of c-erB-1 and c-abl proto-oncogenes may have a role in preimplantation embryonic development in mice.

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.

En bloc substitution of the Src homology region 2 domain activates the transforming potential of the c-Abl protein tyrosine kinase

Src homology region 2 (SH2) domains are present in many proteins involved in signal transduction. In nonreceptor protein tyrosine kinases the SH2 domain has been implicated in regulation of tyrosine kinase activity and in mediating interactions involved in downstream signaling. Different SH2 domains exhibit distinct binding specificities for both phosphotyrosine- and phosphoserine/phosphothreonine-containing proteins. We show that different SH2 domains are not functionally equivalent within the context of the c-ABL1b protooncogene. c-ABL1b, altered by replacement of its SH2 domain with the N-terminal SH2 domain of Ras GTPase-activating protein, exhibited activated transforming capability, caused intracellular tyrosine phosphorylation of p62, and was relocalized from nucleus to cytoplasm. This en bloc substitution apparently uncouples two distinct functions of the SH2 domain so that c-ABL escapes normal regulatory control while it retains the capability to elicit signals that promote transformation. The SH2 domain of the ARG protein tyrosine kinase, which shares high amino acid-sequence homology with the SH2 domain of ABL, was less effective in activating the oncogenic potential of c-ABL. The effects that the N-terminal SH2 domain of Ras GTPase-activating protein has in the context of c-ABL resemble the effects of deleting the SH3 domain. Thus, the SH2 and SH3 domains may have coordinate roles as regulatory control elements within the context of c-ABL.

SH1 domain autophosphorylation of P210 BCR/ABL is required for transformation but not growth factor independence

P210 BCR/ABL is a chimeric oncogene implicated in the pathogenesis of chronic myelogenous leukemia. BCR sequences have been shown to be required for activation of the tyrosine kinase and transforming functions of BCR/ABL. In this work, we show that two other structural requirements for full transforming activity of P210 BCR/ABL include a functional tyrosine kinase and the presence of tyrosine 1294, a site of autophosphorylation within the tyrosine kinase domain. Replacement of tyrosine 1294 with phenylalanine (1294F) greatly diminishes the transforming activity of BCR/ABL without affecting the specific activity of the protein tyrosine kinase. Expression of an exogenous myc gene in fibroblasts partially complements the transforming capacity of mutant P210 BCR/ABL (1294F). Surprisingly, tyrosine 1294 is not required for efficient induction of growth factor-independence in hematopoietic cell lines by P210 BCR/ABL. These results suggest that autophosphorylation at tyrosine 1294 may be important for recognition and phosphorylation of cellular substrates in the pathway of transformation, but it is not critical for mediating the events which lead to growth factor independence.

SH1 domain autophosphorylation of P210 BCR/ABL is required for transformation but not growth factor independence

P210 BCR/ABL is a chimeric oncogene implicated in the pathogenesis of chronic myelogenous leukemia. BCR sequences have been shown to be required for activation of the tyrosine kinase and transforming functions of BCR/ABL. In this work, we show that two other structural requirements for full transforming activity of P210 BCR/ABL include a functional tyrosine kinase and the presence of tyrosine 1294, a site of autophosphorylation within the tyrosine kinase domain. Replacement of tyrosine 1294 with phenylalanine (1294F) greatly diminishes the transforming activity of BCR/ABL without affecting the specific activity of the protein tyrosine kinase. Expression of an exogenous myc gene in fibroblasts partially complements the transforming capacity of mutant P210 BCR/ABL (1294F). Surprisingly, tyrosine 1294 is not required for efficient induction of growth factor-independence in hematopoietic cell lines by P210 BCR/ABL. These results suggest that autophosphorylation at tyrosine 1294 may be important for recognition and phosphorylation of cellular substrates in the pathway of transformation, but it is not critical for mediating the events which lead to growth factor independence.

Transplantability and MHC antigen expression of tumor mast cells

A cloned cell line was established from tumor cells spontaneously developed in a coculture of an autoreactive T cell line (1/+ T1) and 30 Gy-irradiated MRL/+ spleen cells with Con A supernatants. Morphological studies and studies of histamine content and modes of histamine release after stimulation with compound 48/80 revealed that the cell line (MRL-MC3) had mast cell characteristics. MRL-MC3 was transplantable not only to MRL/+, MRL/lpr and AKR/J (H-2k) mice but also to BALB/c and (BALB/c x DBA/2) F1 (H-2d) mice, although the allogeneic mice survived twice as long as syngeneic mice after i.v. injection. In addition, after i.v. injection, the mast cells infiltrated the livers and spleens of syngeneic (MRL/+) mice, however the lymph nodes around the mesenterium to the parapylorus in allogeneic (BALB/c) mice. A mast cell line (BALB-MC) was also established from a lymph node of MRL-MC3-injected BALB/c mice. Cell surface marker analyses revealed clear differences between the BALB-MC and the original MRL-MC3, which was positive for the expression of MHC class I antigens (K, D), I-E antigen and c-abl-encoded (anti-pEX-2 antibody-reactive) proteins, but not for I-A on the cell surface. In contrast, BALB-MC showed positive only for the MHC class I antigens (K, D) on the surface, and also positive for anti-pEX-2 antibody-reactive cytoplasmic proteins, as seen in MRL-MC3. Mast cells obtained from MRL-MC3-injected MRL/+ mice showed the same staining pattern as MRL-MC3. BALB-MC induced shorter survival times (approximately half) in both MRL/+ and BALB/c mice than MRL-MC3.(ABSTRACT TRUNCATED AT 250 WORDS)

Point mutations in the abl SH2 domain coordinately impair phosphotyrosine binding in vitro and transforming activity in vivo

We have constructed a series of point mutations in the highly conserved FLVRES motif of the src homology 2 (SH2) domain of the abl tyrosine kinase. Mutant SH2 domains were expressed in bacteria, and their ability to bind to tyrosine-phosphorylated proteins was examined in vitro. Three mutants were greatly reduced in their ability to bind both phosphotyrosine itself and tyrosine-phosphorylated cellular proteins. All of the mutants that retained activity bound to the same set of tyrosine-phosphorylated proteins as did the wild type, suggesting that binding specificity was unaffected. These results implicate the FLVRES motif in direct binding to phosphotyrosine. When the mutant SH2 domains were inserted into an activated abl kinase and expressed in murine fibroblasts, decreased in vitro phosphotyrosine binding correlated with decreased transforming ability. This finding implies that SH2-phosphotyrosine interactions are involved in transmission of positive growth signals by the nonreceptor tyrosine kinases, most likely via the assembly of multiprotein complexes with other tyrosine-phosphorylated proteins.

Point mutations in the abl SH2 domain coordinately impair phosphotyrosine binding in vitro and transforming activity in vivo

We have constructed a series of point mutations in the highly conserved FLVRES motif of the src homology 2 (SH2) domain of the abl tyrosine kinase. Mutant SH2 domains were expressed in bacteria, and their ability to bind to tyrosine-phosphorylated proteins was examined in vitro. Three mutants were greatly reduced in their ability to bind both phosphotyrosine itself and tyrosine-phosphorylated cellular proteins. All of the mutants that retained activity bound to the same set of tyrosine-phosphorylated proteins as did the wild type, suggesting that binding specificity was unaffected. These results implicate the FLVRES motif in direct binding to phosphotyrosine. When the mutant SH2 domains were inserted into an activated abl kinase and expressed in murine fibroblasts, decreased in vitro phosphotyrosine binding correlated with decreased transforming ability. This finding implies that SH2-phosphotyrosine interactions are involved in transmission of positive growth signals by the nonreceptor tyrosine kinases, most likely via the assembly of multiprotein complexes with other tyrosine-phosphorylated proteins.

Evidence for regulation of the human ABL tyrosine kinase by a cellular inhibitor

Phosphotyrosine cannot be detected on normal human ABL protein-tyrosine kinases, but activated oncogenic forms of the human ABL protein are phosphorylated on tyrosine in vivo. Activation of ABL can occur by substitution of the ABL first exon with breakpoint cluster region (BCR) sequences or by deletion of the noncatalytic SH3 (src homology region 3) domain. An alternative mode for the activation of the ABL kinases is hyperexpression at greater than 500-fold over endogenous levels. This is not a consequence of transphosphorylation of the hyperexpressed ABL molecules. ABL proteins translated in vitro lack phosphotyrosine, but tyrosine kinase activity is uncovered after immunoprecipitation and removal of lysate components. The rates of dephosphorylation of ABL and BCR-ABL fusion protein by phosphotyrosine-specific phosphatases are approximately the same. These combined results indicate that inhibition of ABL activity is reversible and suggest that a cellular component interacts noncovalently with ABL to inhibit its autophosphorylation.

Neonatal lethality and lymphopenia in mice with a homozygous disruption of the c-abl proto-oncogene

The c-abl proto-oncogene, which encodes a cytoplasmic protein-tyrosine kinase, is expressed throughout murine gestation and ubiquitously in adult mouse tissues. However, its levels are highest in thymus, spleen, and testes. To examine the in vivo role of c-abl, the gene was disrupted in embryonic stem cells, and the resulting genetically modified cells were used to establish a mouse strain carrying the mutation. Most mice homozygous for the c-abl mutation became runted and died 1 to 2 weeks after birth. In addition, many showed thymic and splenic atrophy and a T and B cell lymphopenia.

BCR first exon sequences specifically activate the BCR/ABL tyrosine kinase oncogene of Philadelphia chromosome-positive human leukemias

The c-abl proto-oncogene encodes a cytoplasmic tyrosine kinase which is homologous to the src gene product in its kinase domain and in the upstream kinase regulatory domains SH2 (src homology region 2) and SH3 (src homology region 3). The murine v-abl oncogene product has lost the SH3 domain as a consequence of N-terminal fusion of gag sequences. Deletion of the SH3 domain is sufficient to render the murine c-abl proto-oncogene product transforming when myristylated N-terminal membrane localization sequences are also present. In contrast, the human BCR/ABL oncogene of the Philadelphia chromosome translocation has an intact SH3 domain and its product is not myristylated at the N terminus. To analyze the contribution of BCR-encoded sequences to BCR/ABL-mediated transformation, the effects of a series of deletions and substitutions were assessed in fibroblast and hematopoietic-cell transformation assays. BCR first-exon sequences specifically potentiate transformation and tyrosine kinase activation when they are fused to the second exon of otherwise intact c-ABL. This suggests that BCR-encoded sequences specifically interfere with negative regulation of the ABL-encoded tyrosine kinase, which would represent a novel mechanism for the activation of nonreceptor tyrosine kinase-encoding proto-oncogenes.

BCR first exon sequences specifically activate the BCR/ABL tyrosine kinase oncogene of Philadelphia chromosome-positive human leukemias

The c-abl proto-oncogene encodes a cytoplasmic tyrosine kinase which is homologous to the src gene product in its kinase domain and in the upstream kinase regulatory domains SH2 (src homology region 2) and SH3 (src homology region 3). The murine v-abl oncogene product has lost the SH3 domain as a consequence of N-terminal fusion of gag sequences. Deletion of the SH3 domain is sufficient to render the murine c-abl proto-oncogene product transforming when myristylated N-terminal membrane localization sequences are also present. In contrast, the human BCR/ABL oncogene of the Philadelphia chromosome translocation has an intact SH3 domain and its product is not myristylated at the N terminus. To analyze the contribution of BCR-encoded sequences to BCR/ABL-mediated transformation, the effects of a series of deletions and substitutions were assessed in fibroblast and hematopoietic-cell transformation assays. BCR first-exon sequences specifically potentiate transformation and tyrosine kinase activation when they are fused to the second exon of otherwise intact c-ABL. This suggests that BCR-encoded sequences specifically interfere with negative regulation of the ABL-encoded tyrosine kinase, which would represent a novel mechanism for the activation of nonreceptor tyrosine kinase-encoding proto-oncogenes.

Temperature-sensitive mutants of Abelson murine leukemia virus deficient in protein tyrosine kinase activity

The effect of two missense mutations in abl on transformation by Abelson murine leukemia virus was evaluated. These mutations led to the substitution of a histidine for Tyr-590 and a glycine for Lys-536. Both changes gave rise to strains that were temperature dependent for transformation of both NIH 3T3 cells and lymphoid cells when expressed in the context of a truncated Abelson protein. In the context of the prototype P120 v-abl protein, the Gly-536 substitution generated a host range mutant that induced conditional transformation in lymphoid cells but had only a subtle effect on NIH 3T3 cells. The combination of both substitutions gave rise to a P120 strain that was temperature sensitive for both NIH 3T3 and lymphoid cell transformation. The Abelson proteins encoded by the temperature-sensitive strain displayed in vitro kinase activities that were reduced when compared with those of wild-type proteins. In vivo, levels of phosphotyrosine were reduced only at the restrictive temperature. Analysis of cells expressing either the wild-type P160 v-abl protein or the P210 bcr/abl protein and an Abelson protein encoded by a temperature-sensitive strain failed to correct this defect, suggesting either that tyrosine phosphorylation in vivo is an intramolecular reaction or that the protein encoded by the temperature-sensitive strain is a poor substrate for tyrosine phosphorylation in vivo. These results raise the possibility that tyrosine phosphorylation of Abelson protein plays a role in transformation.

bcr/abl and src but not myc and ras replace v-abl in lymphoid transformation

Lymphoid cells transformed by temperature-sensitive Abelson virus die at the nonpermissive temperature. This property was exploited to show that bcr/abl and v-src but not myc and ras can replace the transforming signal of v-abl, a result suggesting that the former but not the latter oncogenes transform lymphoid cells via a similar pathway.

bcr/abl and src but not myc and ras replace v-abl in lymphoid transformation

Lymphoid cells transformed by temperature-sensitive Abelson virus die at the nonpermissive temperature. This property was exploited to show that bcr/abl and v-src but not myc and ras can replace the transforming signal of v-abl, a result suggesting that the former but not the latter oncogenes transform lymphoid cells via a similar pathway.

The mouse type IV c-abl gene product is a nuclear protein, and activation of transforming ability is associated with cytoplasmic localization

The subcellular localization of the mouse type IV c-abl protein was determined by indirect immunofluorescence of nontransformed NIH 3T3 fibroblasts that overexpress the protein. Unlike the viral transforming protein p160gag/v-abl, which has cytoplasmic and plasma membrane localization, a large fraction of the c-abl (IV) protein is nuclear, with the remainder in the cytoplasm and plasma membrane. Deletion of a small N-terminal regulatory region of the c-abl (IV) protein, sufficient to activate its transforming potential fully, changes the distribution of the protein from the nucleus to the cytoplasm. Mapping of an amino acid sequence responsible for the nuclear localization of the c-abl (IV) protein reveals a nuclear localization signal similar to that of SV40 large T antigen.

The viral and cellular forms of the Abelson (abl) oncogene

The precision of molecular biology has allowed a better definition of the components of the Abelson system. We know the gene structures and gene products for the cellular and viral forms of this family of related tyrosine kinases. However, many basic issues first identified in the early biological observations of Abelson, Rabstein, and others remain unanswered. The precise pathway for transformation in biochemical terms remains unknown for Ab-MLV and all of its relatives. Relatively little can be said to explain the preferential growth stimulation for certain hematopoietic cell types by the viral and other altered forms of the oncogene, and no clear insights into the function of the normal cellular forms of the abl oncogene are available. Future progress will certainly depend on the intensive efforts by many workers in the broader field of cellular growth control mechanisms.

Gag-derived but not abl-derived determinants are exposed on the surface of Abelson virus-transformed cells

The organization of the transforming protein encoded by Abelson murine leukemia virus (A-MuLV) in transformed lymphoid and fibroblast cells was examined using immunofluorescent analysis. Antibodies specific for v-abl were capable of detecting cytoplasmic Abelson protein molecules in fixed cells, but none were able to stain the surface of live A-MuLV transformed cells. However, a series of monoclonal antibodies selected for the ability to bind to the surface of A-MuLV-transformed cells did stain live cells. These antibodies were shown to react with a determinant within the helper virus-derived p15 sequences that are present at the amino terminus of the Abelson protein, indicating that gag-derived determinants are exposed on the surface of transformed cells. The inability of a p12-specific monoclonal antibody to stain live cells indicates that only a small portion of the amino terminal sequences are exposed. Examination of the ability of these antibodies to react with Abelson protein encoded by a series of gag deletion mutants suggests that the determinant recognized by these antibodies lies between amino acids 38 and 114 of p15.

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

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

Abelson virus drives the differentiation of Harvey virus-infected erythroid cells

Abelson murine leukemia virus (A-MuLV) and Harvey murine sarcoma virus (Ha-MSV) are retroviruses carrying unrelated onc genes. However, both of these viruses are capable of stimulating the growth and differentiation of erythroid precursor cells; the target cells for both appear at the same time during fetal development and follow a similar pattern throughout ontogeny. In addition, the colonies induced by each virus are morphologically similar and synthesize the adult form of hemoglobin. However, A-MuLV-infected cells are Epo-independent, whereas Ha-MSV-infected cells are Epo-dependent. Superinfection of Ha-MSV-infected cells with A-MuLV overrides their Epo-dependency. Thus, the consequences of the infection are determined by the interaction of the different onc gene products with identical or similar erythroid cells.