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O N Witte

Publications and source records attributed to O N Witte.

At least 163 records · Page 9Linked to original sources
PubMed1987

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.

Amino Acid Sequence↗
PubMed1986

Lymphoid bone marrow cultures can reconstitute heterogeneous B and T cell-dependent responses in severe combined immunodeficient mice.

Long-term lymphoid bone marrow cultures (LBMC) produce B lymphocytes and their precursors for several months in vitro. To assess their differentiative potential and determine their capacity to function as immune effectors, cells from the cultures were transplanted into mice with severe combined immune deficiency disease (SCID). SCID mice are deficient in T and B lymphocytes and are serum immunoglobulin (Ig) negative, but grafts of normal lymphoid precursors can expand and differentiate in them, thereby restoring immunocompetence. The results of these studies indicate that cells from LBMC are able to reconstitute splenic B lymphocytes in the SCID mice. Upon in vivo transfer, LBMC cells secreted Ig that displayed isotype distribution and a pattern of heterogeneity comparable with normal BALB/c mice, as determined by two-dimensional gel electrophoresis. The transplanted LBMC cells were functional, because reconstituted mice could respond to immunization with the T-independent antigen TNP-Ficoll. The results also indicate that cultured cells could reconstitute T cell activity in SCID mice. Splenocytes from approximately one-third of the recipients could generate a cytotoxic response to alloantigens after 5 days of sensitization in a mixed lymphocyte culture, and all reconstituted SCID mice could respond to immunization with the T cell-dependent antigen TNP-BSA. These results demonstrate that B cells, as well as T cell activity, are present in LBMC-reconstituted SCID mice, and show that LBMC cells have the capacity to mediate an immune response.

Animals↗
PubMed1986

Corticosteroid-resistant bone marrow-derived B lymphocyte progenitor for long term in vitro cultures.

A long-term in vitro culture system derived from murine bone marrow cells can successfully support the growth of B cell precursors, pre-B cells, and IgM-expressing B cells. Intermediates in the B cell developmental pathway are known to have differential sensitivities to the toxic effects of corticosteroids. We demonstrate here that long term B lineage cultures can be established with the corticosteroid-resistant cell population from bone marrow. Kinetics for the establishment and growth of cultures derived from corticosteroid-treated marrow are similar to those observed with control cultures. Cells obtained from both sets of cultures have similar morphologies and ranges of phenotypic markers. These results indicate that the cell responsible for the outgrowth of the long term B lineage cultures is corticosteroid resistant and is likely to be earlier in the B lymphocyte lineage than steroid-sensitive pre-B cells.

Abelson murine leukemia virus↗
PubMed1986

The chronic myelogenous leukemia-specific P210 protein is the product of the bcr/abl hybrid gene.

Chronic myelogenous leukemia (CML) is a human disease associated with a consistent chromosomal translocation that results in sequences from the c-abl locus on chromosome 9 being fused to sequences in a breakpoint cluster region (bcr) on chromosome 22. CML cells have two novel products: an 8.5-kilobase RNA transcript containing both abl and bcr and a 210-kilodalton phosphoprotein (P210) recognized by v-abl-specific antisera. To test whether the P210 is the product of the novel 8.5-kilobase bcr/abl fusion transcript, antibodies were prepared against c-abl and bcr determinants. By using these reagents and v-abl-specific antisera, it was demonstrated that the P210 in CML cells is indeed the protein product of the 8.5-kilobase transcript. By analogy to the gag/abl fusion protein of Abelson murine leukemia virus, the replacement of amino terminal c-abl sequences by bcr sequences in P210 may create a transforming protein involved in CML. A 190-kilodalton phosphoprotein that is a candidate for the normal bcr protein was identified in both HeLa and K562 cells.

Abelson murine leukemia virus↗
PubMed1986

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.

B-Lymphocytes↗
PubMed1986

In vitro development of B lymphocytes from long-term cultured precursor cells.

An in vitro system for the study of B-lymphocyte differentiation from precursor elements has been established. Two separate sets of culture conditions are utilized to control B-lymphocyte precursor growth versus differentiation. The first, modeled after the bone marrow culture system of Dexter and colleagues [Dexter, T. M. & Testa, N. G. (1976) in Methods in Cell Biology, ed. Prescott, D. M. (Academic, New York), Vol. 14, pp. 387-395], allows precursor replication whereas the second set of culture conditions is permissive for differentiation to more mature members of the B-lymphocyte lineage. The shift from one set of conditions to the other allows us to follow the kinetics of this differentiation from precursor cells to pre-B and B lymphocytes over a 5-week period. The resulting population of B-lineage cells synthesizes heterogeneous immunoglobulin molecules as analyzed by two-dimensional gel electrophoresis and has a heterogeneous array of immunoglobulin gene rearrangements, suggesting an origin from very early uncommitted precursors. This in vitro system will allow the study of genes that regulate B-lymphocyte differentiation and will aid in the isolation of the cellular intermediates in the B-cell developmental pathway.

Animals↗
PubMed1986

Overlapping cDNA clones define the complete coding region for the P210c-abl gene product associated with chronic myelogenous leukemia cells containing the Philadelphia chromosome.

The Philadelphia chromosome, observed in greater than 90% of patients with chronic myelogenous leukemia, results from a reciprocal translocation between chromosomes 9 and 22. The translocation breakpoint on chromosome 9 occurs near the ABL gene and correlates with the production of a chronic myelogenous leukemia-specific 8.5-kilobase ABL-related mRNA species accompanied by a structurally altered ABL protein (P210c-abl). The N-terminal sequence of the protein is derived from the BCR gene on chromosome 22. We have isolated overlapping cDNA clones from the K-562 cell line corresponding to approximately 8.5 kilobases of mRNA and have sequenced 2550 nucleotides at the 5' end. Our results indicate that the 5' end of the 8.5-kilobase mRNA consists of greater than 400 nucleotides of noncoding sequence that are greater than 80% G + C rich. Based on our sequence analysis, we propose that initiation of translation occurs at nucleotide 471, such that the initial 927 amino acids of P210c-abl are derived from BCR sequences. Our cDNA clones thus define the complete coding sequences for the P210c-abl gene product.

Base Sequence↗
PubMed1986

Monoclonal antibody to the amino-terminal L sequence of murine leukemia virus glycosylated gag polyproteins demonstrates their unusual orientation in the cell membrane.

To analyze cell surface murine leukemia virus gag protein expression, we have prepared monoclonal antibodies against the spontaneous AKR T lymphoma KKT-2. One of these antibodies, 43-13, detects an AKR-specific viral p12 determinant. A second monoclonal antibody, 43-17, detects a novel murine leukemia virus-related antigen found on glycosylated gag polyproteins (gp95gag, gp85gag, and gp55gag) on the surface of cells infected with and producing ecotropic endogenous viruses, but does not detect antigens within these virions. The 43-17 antibody immunoprecipitates the precursor of the cell surface gag protein whether in its glycosylated or unglycosylated state, but does not detect the cytoplasmic precursor of the virion gag proteins (Pr65gag). Based on these findings, we have localized the 43-17 determinant to the unique amino-terminal part of the glycosylated gag polyprotein (the L domain). We have determined that gp95gag contains L-p15-p12-p30-p10 determinants, whereas gp85gag lacks the carboxyterminal p10 determinant, and gp55gag lacks both p30 and p10 carboxy terminal determinants. Analysis of cell surface gag expression with the 43-17 antibody leads us to propose that the L domain plays a crucial role in (i) the insertion and orientation of murine leukemia virus gag polyproteins in the cell membrane and (ii) the relative abundance of expression of AKR leukemia virus versus Moloney murine leukemia virus glycosylated gag polyproteins in infected cells.

Animals↗
PubMed1986

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

Monoclonal antibodies specific for regions of the transforming protein of Abelson murine leukemia virus were prepared. Antibodies directed against the kinase domain inhibited the autophosphorylation of v-abl proteins, and all of the antibodies reacted with the products of the murine and human c-abl loci.

Abelson murine leukemia virus↗
PubMed1986

Synergism of v-myc and v-Ha-ras in the in vitro neoplastic progression of murine lymphoid cells.

Murine bone marrow was either singly or doubly infected with retroviral vectors expressing v-myc (OK10) or v-Ha-ras. The infected bone marrow was cultured in a system that supports the long-term growth of B-lineage lymphoid cells. While the v-myc vector by itself had no apparent effect on lymphoid culture establishment and growth, infection with the v-Ha-ras vector or coinfection with both v-myc and v-Ha-ras vectors led to the appearance of growth-stimulated cell populations. Clonal pre-B-cell lines stably expressing v-Ha-ras alone or both v-myc and v-Ha-ras grew out of these cultures. In comparison with cell lines expressing v-Ha-ras alone, cell lines expressing both v-myc and v-Ha-ras grew to higher densities, had reduced dependence on a feeder layer for growth, and had a marked increase in ability to grow in soft-agar medium. The cell lines expressing both oncogenes were highly tumorigenic in syngeneic animals. These experiments show that the v-myc oncogene in synergy with v-Ha-ras can play a direct role in the in vitro transformation of murine B lymphoid cells.

Animals↗
PubMed1986

Involvement of the abl oncogene in human chronic myelogenous leukemia.

The Philadelphia chromosome found in essentially all patients with chronic myelogenous leukemia is now known to express a chimeric mRNA of 8.5 kb derived from sequences on chromosome 22 and sequences on chromosome 9. The chromosome 9 component of the chimeric RNA is derived from a subset of the exons of the abl oncogene. A portion of the exonic sequences of a gene referred to as bcr on chromosome 22 make up the amino-terminal portion of this chimeric mRNA and gene product. Our laboratory has recently succeeded in obtaining full-length clones of the 8.5 kb mRNA. The sequence analysis of this large mRNA reveals an exceptionally G-C rich 5' untranslated region. A complete open reading frame initiating in sequences of the bcr gene and reading through the abl oncogene segment has been determined. The sequence also reveals an extremely high percentage of serine residues in the bcr segment of the chimeric protein.

Humans↗
PubMed1986

Functions of the abl oncogene.

The cellular abl oncogene and those derived by viral transduction and chromosomal translocation events encode a family of closely related proteins with intrinsic tyrosine kinase activity. The known in vitro and in vivo manifestations of these tyrosine specific kinase activities are, in general, very similar to those of other members of the src gene family. The expression of the normal c-abl messages and gene products is not remarkably different among most tissues, including the haemolymphoid system. However, the broad haemopoietic transformation spectrum of the murine v-abl protein and the association of the abl oncogene with human chronic myelogenous leukaemia suggest that some special structure-function relationship for the abl protein might hold for the growth regulation of blood forming cells. This article concentrates on recent data that have pointed the way toward several testable models for the intracellular behaviour of the c-abl proteins and their altered counterparts which function in cellular transformation and other altered growth states. More detailed review articles which cover the historical development of the field (Baltimore et al, 1979; Rosenberg and Baltimore, 1980), biological properties of the Abelson murine leukaemia virus (Risser, 1982; Whitlock and Witte, 1985) and the structure of the abl gene and its products (Witte, 1983; Konopka and Witte, 1985a) are available.

Animals↗
PubMed1985

Cell lines and clinical isolates derived from Ph1-positive chronic myelogenous leukemia patients express c-abl proteins with a common structural alteration.

The Philadelphia chromosome (Ph1), observed in greater than 90% of chronic myelogenous leukemia (CML) patients, results from a specific chromosomal translocation involving the c-abl gene. The translocation breakpoint occurs near c-abl and correlates with the production of an altered c-abl mRNA. In the CML-derived cell line K562, Ph1 is accompanied by a structurally altered c-abl protein (P210c-abl) with in vitro tyrosine kinase activity not detected with the normal c-abl protein (P145c-abl). We have examined c-abl proteins in other Ph1-positive CML cell lines and found that they all express P210c-abl. P210c-abl was also detected in bone marrow cells from CML patients with Ph1 in the accelerated and blast crisis phases of the disease. Comparison of the [35S]methionine-labeled tryptic peptides generated from the normal P145c-abl and P210c-abl showed that they have closely related structures, but additional polypeptide sequences are present in P210c-abl. Based on these results we propose that translocation of c-abl in Ph1-positive CML results in the creation of a chimeric gene leading to the production of a structurally altered c-abl protein with activated tyrosine kinase activity. The altered P210 c-abl protein is strongly implicated in the pathogenesis of CML.

Cell Line↗
PubMed1985

Activation of the c-abl oncogene by viral transduction or chromosomal translocation generates altered c-abl proteins with similar in vitro kinase properties.

The v-abl protein of Abelson murine leukemia virus is a tyrosine-specific kinase. Its normal cellular homolog, murine c-abl, does not possess detectable tyrosine kinase activity in vitro. Previously, we have detected tyrosine kinase activity in vitro for an altered c-abl gene product (c-abl P210) in the K562 human chronic myelogenous leukemia cell line. The expression of this variant c-abl gene product correlates with chromosomal translocation and amplification of the c-abl gene in K562 cells. Like v-abl, c-abl P210 is a fusion protein containing non-abl sequences near the amino terminus of c-abl. We compared the in vitro tyrosine kinase activity of c-abl P210 with that of wild-type murine v-abl. The remarkable similarities of these two proteins with respect to cis-acting autophosphorylation, trans-acting phosphorylation of exogenous substrates, and kinase inhibition, using site-directed abl-specific antisera, suggested that c-abl P210 could function similarly to v-abl in vivo. In addition, c-abl P210 possessed an associated serine kinase activity in immunoprecipitates. The serine kinase activity was not inhibited by site-directed, abl-specific antisera that inhibit the tyrosine kinase activity, suggesting that the serine kinase activity is not an intrinsic property of c-abl P210. Thus, the activation of the c-abl gene in a human leukemia cell line may have functional consequences analogous to activation of the c-abl gene in Abelson murine leukemia virus.

Abelson murine leukemia virus↗