Biomedical subjects

O N Witte

Publications and source records attributed to O N Witte.

At least 55 records · Page 3Linked to original sources

PubMed1998

Development of acute lymphoblastic leukemia and myeloproliferative disorder in transgenic mice expressing p210bcr/abl: a novel transgenic model for human Ph1-positive leukemias.

The Philadelphia (Ph) chromosome can be detected in chronic myelogenous leukemia (CML) and a significant number of acute lymphoblastic leukemia (ALL) cases. Generation of p210bcr/abl, a chimeric protein with enhanced kinase activity, is thought to be involved in the pathogenesis of these diseases. To elucidate the biological properties of p210bcr/abl and to create an animal model for human Ph1-positive leukemias, we generated transgenic mice expressing p210bcr/abl driven by the promoter of the tec gene, a cytoplasmic tyrosine-kinase preferentially expressed in the hematopoietic lineage. The founder mice showed excessive proliferation of lymphoblasts shortly after birth and were diagnosed as suffering from ALL based on surface marker and Southern blot analyses. Expression and enhanced kinase activity of the p210bcr/abl transgene product were detected in the leukemic tissues. In contrast, transgenic progeny exhibited marked granulocyte hyperplasia with thrombocytosis after a long latent period and developed myeloproliferative disorders (MPDs) closely resembling human CML. Expression of p210(bcr/abl) mRNA in the proliferating granulocytes was detected by RT-PCR. In particular, one MPD mouse showed remarkable proliferation of blast cells in the lung, which might represent an extramedullar blast crisis. The results demonstrate that the expression of p210bcr/abl in hematopoietic progenitor cells in transgenic mice can contribute to two clinically distinct hematopoietic malignancies, CML and ALL, indicating that this transgenic system provides a novel transgenic model for human Ph1-positive leukemias.

Animals↗

PubMed1998

Prostate stem cell antigen: a cell surface marker overexpressed in prostate cancer.

The identification of cell surface antigens is critical to the development of new diagnostic and therapeutic modalities for the management of prostate cancer. Prostate stem cell antigen (PSCA) is a prostate-specific gene with 30% homology to stem cell antigen 2, a member of the Thy-1/Ly-6 family of glycosylphosphatidylinositol (GPI)-anchored cell surface antigens. PSCA encodes a 123-aa protein with an amino-terminal signal sequence, a carboxyl-terminal GPI-anchoring sequence, and multiple N-glycosylation sites. PSCA mRNA expression is prostate-specific in normal male tissues and is highly up-regulated in both androgen-dependent and -independent prostate cancer xenografts. In situ mRNA analysis localizes PSCA expression in normal prostate to the basal cell epithelium, the putative stem cell compartment of the prostate. There is moderate to strong PSCA expression in 111 of 126 (88%) prostate cancer specimens examined by in situ analysis, including high-grade prostatic intraepithelial neoplasia and androgen-dependent and androgen-independent tumors. Flow cytometric analysis demonstrates that PSCA is expressed predominantly on the cell surface and is anchored by a GPI linkage. Fluorescent in situ hybridization analysis localizes the PSCA gene to chromosome 8q24.2, a region of allelic gain in more than 80% of prostate cancers. A mouse homologue with 70% amino acid identity and similar genomic organization to human PSCA has also been identified. These results support PSCA as a target for prostate cancer diagnosis and therapy.

Amino Acid Sequence↗

PubMed1998

Regional gene therapy with a BMP-2-producing murine stromal cell line induces heterotopic and orthotopic bone formation in rodents.

The ability to continuously deliver osteoinductive proteins to a specific anatomic site would facilitate the treatment of fracture nonunions and other clinical problems associated with bone loss. We have developed a murine model of regional gene therapy. A bone-marrow stromal cell line infected with an adenovirus expressing recombinant bone morphogenetic protein-2 cDNA secreted biologically active bone morphogenetic protein-2. These bone morphogenetic protein-2-producing cells were able to induce abundant heterotopic bone formation when implanted into the quadriceps muscle of severe combined immune deficient mice and also successfully healed large segmental femoral defects in nude rats. These studies demonstrate that regional gene therapy with continuous delivery of osteoinductive factors to a specific anatomic site can enhance the formation and repair of bone.

Animals↗

PubMed1998

Btk function in B cell development and response.

Mutations in Bruton's tyrosine kinase (Btk) result in the B cell immunodeficiencies XLA in humans and Xid in mice. Both the maintenance of peripheral B cell numbers and their response to B cell antigen receptor (BCR) crosslinking depend on Btk. Btk integrates signals from multiple cell surface receptors, including BCR and G-protein coupled receptors. These Btk dependent signals control B cell proliferation and survival by mediating Ca2+ flux, activating JNK and p38 and inducing cell cycle regulatory genes.

Agammaglobulinaemia Tyrosine Kinase↗

PubMed1998

Dissection of signaling pathways and cloning of new signal transducers in tyrosine kinase-induced pathways by genetic selection.

We used genetic strategies which have been proven valuable to decipher signaling pathways in comparatively simple organisms such as Drosophila and Caenorhabditis elegans, to dissect signaling network activated by tyrosine kinases in mammals. The strategy was developed further towards a generally applicable expression cloning system to identify signal transducers in tyrosine kinase pathways. This system is based on the ability of downstream acting genes to rescue the transformation phenotype of partial loss-of-function mutants of BCR-ABL which still retain tyrosine kinase activity. Using this strategy we have previously shown that overexpression of c-Myc and Cyclin D1 can rescue a signaling defective SH2 mutant of BCR-ABL for transformation. In an unbiased approach to identify new compensating genes, a cDNA library was introduced by retroviral infection into fibroblasts which express the BCR-ABL SH2 mutant. CDNA clones, capable of rescuing the SH2 mutant for transformation should result in colony formation in soft agar. A PCR approach was used to recover these compensating genes from the genomic DNA of the transformed fibroblasts. Sequencing analysis of the initial cDNAs identified three known genes, the adapter molecule Shc, the kinases SPRK and p38 MAPK. These genes have been found to interact functionally with BCR-ABL for fibroblast and hematopoietic cell transformation. Currently, we are constructing and screening new libraries to identify novel genes which complement the BCR-ABL SH2 mutant. Our results demonstrate that this cloning approach is an effective means of identifying and characterizing signaling molecules that function in specific signaling pathways. This in turn may identify specific targets for mechanism-based therapeutic intervention to block altered signaling.

Adaptor Proteins, Signal Transducing↗

PubMed1998

Bcl-2-independent Bcr-Abl-mediated resistance to apoptosis: protection is correlated with up regulation of Bcl-xL.

Bcr - Abl is the molecule responsible for both the transformation phenotype and the resistance to chemotherapeutic drugs found in chronic myelogenous leukemia (CML) cells. Wild-type HL-60, a transformed pro-myelocytic cell line, is very susceptible to apoptosis-inducing agents. We show here that expression of Bcr - Abl in HL-60 cells rendered them extremely resistant to apoptosis induced by a wide variety of agents. The anti-apoptotic effect of Bcr - Abl was found to be independent of the phase of the cell cycle. Treatment with antisense oligonucleotides directed to bcr decreased the expression of the ectopic bcr - abl and restored susceptibility to apoptosis. Double mutations affecting the autophosphorylation site and the phosphotyrosine-binding motif (FLVRES) have been previously shown to impair the transforming activity of Bcr - Abl in fibroblasts and hematopoietic cells, however HL-60 cells expressing this double mutant molecule exhibited the same level of resistance to apoptosis as those expressing the wild-type Bcr - Abl. Interestingly, wild type and mutant Bcr - Abl induced in HL-60 cells a dramatic down regulation of Bcl-2 and increased the levels of Bcl-xL. The level of Bax did not change in response to the presence of Bcr - Abl. Antisense oligonucleotides targeted to bcl-x downregulated the expression of Bcl-x, and increased the susceptibility of HL-60. Bcr - Abl cells to staurosporine. Importantly, HL-60 cells overexpressing Bcl-xL showed higher expression of Bcl-xL but lower resistance to apoptosis when compared to HL-60. Bcr - Abl cells. The results described here show that Bcr - Abl is a powerful mammalian anti-apoptotic molecule and can act independently of Bcl-2. Bcl-xL, however, seems to participate in part in Bcr - Abl-mediated resistance to apoptosis in HL-60 cells.

Apoptosis↗

PubMed1997

Phosphatidylinositol 3-kinase-gamma activates Bruton's tyrosine kinase in concert with Src family kinases.

Bruton's tyrosine kinase (Btk) is essential for normal B lymphocyte development and function. The activity of Btk is partially regulated by transphosphorylation within its kinase domain by Src family kinases at residue Tyr-551 and subsequent autophosphorylation at Tyr-223. Activation correlates with Btk association with cellular membranes. Based on specific loss of function mutations, the Btk pleckstrin homology (PH) domain plays an essential role in this activation process. The Btk PH domain can bind in vitro to several lipid end products of the phosphatidylinositol 3-kinase (PI 3-kinase) family including phosphatidylinositol 3,4,5-trisphosphate. Activation of Btk as monitored by elevation of phosphotyrosine content and a cellular transformation response was dramatically enhanced by coexpressing a weakly activated allele of Src (E378G) and the two subunits of PI 3-kinase-gamma. This activation correlates with new sites of phosphorylation on Btk identified by two-dimensional phosphopeptide mapping. Activation of Btk was dependent on the catalytic activity of all three enzymes and an intact Btk PH domain and Src transphosphorylation site. These combined data define Btk as a downstream target of PI 3-kinase-gamma and Src family kinases.

Agammaglobulinaemia Tyrosine Kinase↗

PubMed1997

Btk dosage determines sensitivity to B cell antigen receptor cross-linking.

Mutations in Btk result in the B cell immunodeficiencies X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency (xid) in mice. Btk is a critical component of signaling pathways regulating B cell development and function. We used a genetic approach to determine whether Btk is also limiting for these processes. One allele of a murine Btk transgene expressed a dosage of Btk (25% of endogenous levels in splenic B cells) sufficient to restore normal numbers of phenotypically mature conventional B cells in xid mice. 2,4,6-trinitrophenyl-Ficoll response, anti-IgM-induced proliferation, B1 cell development, and serum IgM and IgG3 levels remained significantly impaired in these animals. B cells from Btk -/- transgenic mice also responded poorly to anti-IgM, indicating that the xid mutation does not create a dominant negative form of Btk. Response to 2,4,6-trinitrophenyl-Ficoll and B cell receptor cross-linking were increased 3- to 4-fold in xid mice homozygous for the transgene. These results demonstrate that Btk is a limiting component of B cell antigen receptor signaling pathways and suggest that B cell development and response to antigen may require different levels of Btk activity.

Agammaglobulinaemia Tyrosine Kinase↗

PubMed1997

Phosphorylation of two regulatory tyrosine residues in the activation of Bruton's tyrosine kinase via alternative receptors.

Mutation of Bruton's tyrosine kinase (Btk) impairs B cell maturation and function and results in a clinical phenotype of X-linked agammaglobulinemia. Activation of Btk correlates with an increase in the phosphorylation of two regulatory Btk tyrosine residues. Y551 (site 1) within the Src homology type 1 (SH1) domain is transphosphorylated by the Src family tyrosine kinases. Y223 (site 2) is an autophosphorylation site within the Btk SH3 domain. Polyclonal, phosphopeptide-specific antibodies were developed to evaluate the phosphorylation of Btk sites 1 and 2. Crosslinking of the B cell antigen receptor (BCR) or the mast cell Fcepsilon receptor, or interleukin 5 receptor stimulation each induced rapid phosphorylation at Btk sites 1 and 2 in a tightly coupled manner. Btk molecules were singly and doubly tyrosine-phosphorylated. Phosphorylated Btk comprised only a small fraction (</=5%) of the total pool of Btk molecules in the BCR-activated B cells. Increased dosage of Lyn in B cells augmented BCR-induced phosphorylation at both sites. Kinetic analysis supports a sequential activation mechanism in which individual Btk molecules undergo serial transphosphorylation (site 1) then autophosphorylation (site 2), followed by successive dephosphorylation of site 1 then site 2. The phosphorylation of conserved tyrosine residues within structurally related Tec family kinases is likely to regulate their activation.

3T3 Cells↗

PubMed1997

Constitutive membrane association potentiates activation of Bruton tyrosine kinase.

Mutations in the nonreceptor tyrosine kinase Btk result in the B cell immunodeficiencies X-linked agammaglobulinemia (XLA) in humans and X-linked immunodeficiency (xid) in mice. Genetic and biochemical evidence implicates Btk as a key component of several B cell signaling pathways. Activation of Btk by a point mutation (E41K) within the PH domain (Btk*) results in fibroblast transformation and is correlated with increased membrane localization of Btk. When wild type Btk is activated by coexpression with Lyn, the tyrosine phosphorylated pool of Btk is highly enriched in the membrane fraction. To determine whether membrane association is sufficient to activate Btk, we targeted Btk to the plasma membrane using a series of fusion proteins including GagBtk, CD16Btk and CD4Btk. Constitutive membrane association greatly enhanced the ability of Btk to transform Rat2 fibroblasts in the presence of high levels of Src activity. All membrane targeted forms of Btk were highly tyrosine phosphorylated. Transformation required membrane localization, Btk kinase activity, transphosphorylation by Src family kinases, and an intact SH2 domain but not the PH or SH3 domains. These data suggest that membrane localization is a critical early step in Btk activation.

3T3 Cells↗

PubMed1997

Regulation of the oncogenic activity of BCR-ABL by a tightly bound substrate protein RIN1.

RIN1 was originally identified by its ability to physically bind to and interfere with activated Ras in yeast. Paradoxically, RIN1 potentiates the oncogenic activity of the BCR-ABL tyrosine kinase in hematopoietic cells and dramatically accelerates BCR-ABL-induced leukemias in mice. RIN1 rescues BCR-ABL mutants for transformation in a manner distinguishable from the cell cycle regulators c-Myc and cyclin D1 and the Ras connector Shc. These biological effects require tyrosine phosphorylation of RIN1 and binding of RIN1 to the Abl-SH2 and SH3 domains. RIN1 is tyrosine phosphorylated and is associated with BCR-ABL in human and murine leukemic cells. RIN1 exemplifies a new class of effector molecules dependent on the concerted action of the SH3, SH2, and catalytic domains of a cytoplasmic tyrosine kinase.

Adaptor Proteins, Signal Transducing↗

PubMed1997

Progression of metastatic human prostate cancer to androgen independence in immunodeficient SCID mice.

Prostate cancer mortality results from metastasis to bone and hormone-independent tumor growth. Models to study these progressive changes are lacking. Here we describe the propagation of advanced human prostate cancer by direct transfer of surgical samples from patients into immune-deficient male SCID mice. Explants from six of eight patients formed prostate tumors and two showed unique cytogenetic, biologic and molecular features that were retained through six or more passages. One grew in an androgen-independent fashion, whereas the second formed tumors that regressed following castration then regrew. Micrometastatic disease was detected in the hematopoietic tissues of half of the recipient mice. Thus selected specimens of advanced human prostate cancer can be propagated in SCID mice in a manner that recapitulates the clinical transition from androgen-sensitive to androgen-independent growth, accompanied by micrometastasis.

Androgens↗

PubMed1997

Differentiation of human CD34+CD38- cord blood stem cells into B cell progenitors in vitro.

Umbilical cord blood CD34+CD38- cells are a rare, quiescent, primitive progenitor subpopulation lacking expression of lymphoid and myeloid lineage specific antigens. Although myeloid, erythroid, and megakaryocytic differentiation from these cells has been described, B lineage differentiation has not been demonstrated previously. We report here that highly enriched human B cell progenitors can be consistently generated from CD34+CD38- cord blood cells using long-term culture on the murine stromal line, S17, in the absence of added cytokines. After 6-8 weeks, cell numbers increased up to 160-fold, and cultures contained > 80-90% CD10+CD19+ B progenitors. Consistent with previous reports describing delayed myeloid cell differentiation from CD34+CD38- cells, production of B cell progenitors from CD34+CD38- cord blood cells was delayed 2-4 weeks relative to cultures initiated with either CD34+CD38bright or CD34+CD38dim progenitors. Addition of Flt3 ligand to long-term cultures resulted in a 2-3-fold greater increase in the number of CD19+ cells generated after 4-8 weeks. The selective outgrowth of B cell progenitors using this culture model will be useful for a range of in vitro studies using primitive hematopoietic progenitors.

ADP-ribosyl Cyclase↗

PubMed1997

A functional screen for regulators of the c-Abl protein tyrosine kinase.

c-Abl protein tyrosine kinase activity is tightly regulated in vertebrate cells. Several mutations can activate Abl and convert it into an oncogene. In man, chromosomal translocations result in fusion proteins associated with chronic myelogenous leukemias and some acute lymphocytic leukemias. In viral forms of abl, gag sequences are fused to Abl portions resulting in a deletion of N-terminal sequences. To study c-Abl activity in a cellular environment likely to lack specific regulators, we have expressed human c-Abl in Schizosaccharomyces pombe in an inducible fashion. c-Abl causes growth arrest followed by death of the cells. Mutations in the SH2 domain or in the autophosphorylation site dramatically reduce the ability of Abl to confer the growth arrest phenotype and to phosphorylate endogenous proteins, suggesting a fundamental role of these structures in the activity of the enzyme. An SH3 domain deletion mutant of Abl is as active as c-Abl in yeast indicating that there is no intrinsic regulation of c-Abl occurring via the SH3 domain and suggesting that the inhibitory effect of the SH3 domain observed in cells of vertebrate origin is mediated by a factor that is absent in fission yeast. We have used this assay to functionally screen a human cDNA library for molecules able to counteract the lethal effect of c-Abl expression. We are currently in the process of characterising the isolated clones. We hope to identify among them the molecule(s) responsible for regulating c-Abl activity in human cells.

Animals↗

PubMed1996

BCR-ABL induces neurite-like structures and BCR lacking the SH2-binding domain induces cell rounding in PC12 cells.

The activated tyrosine kinase oncoprotein BCR-ABL is responsible for pathogenesis of Philadelphia chromosome-positive human leukemias. Because BCR carries a GAP (GTPase-activating protein) activity toward cytoskeleton-related small GTP-binding proteins, we utilized a neuronal PC12 cell system to test morphogenic potentials of BCR-ABL or BCR. We report here unique morphological phenotypes of PC12 cells expressing either BCR-ABL or a BCR mutant which lacks the SH2-binding domain (BCR Delta162-413). Although MAP kinase was not activated in PC12 cells expressing BCR-ABL, they showed incomplete neurite extensions even in the absence of the nerve growth factor (NGF). Overproduction of BCR Delta162-413 in PC12 cells, on the other hand, induced cell rounding in the absence of NGF. Interestingly, those cells could hardly make terminal differentiation in the presence of NGF and continued to grow without changing their round shape, although NGF receptor as well as MAP kinase appeared to be activated. Interestingly, the botulinum C3 toxin induced neurite-like structures in PC12 cells overexpressing BCR Delta162-413 without NGF.

Animals↗

PubMed1996

The dimerization property of glutathione S-transferase partially reactivates Bcr-Abl lacking the oligomerization domain.

Bcr-Abl oncoproteins are responsible for the pathogenesis of human leukemias with a reciprocal chromosome translocation t(9;22). The amino-terminal Bcr sequence has a potential to form a homotetramer (tetramer domain), and destructions of the tetramer domain cause a complete loss of biological activities in Bcr-Abl. Here we show that Bcr-Abl in which the tetramer domain is replaced with glutathione S-transferase (GST) with a dimerizing ability (GST/Bcr-Abl-(Delta1-160)) can no longer induce an interleukin-3 (IL-3) independence in Ba/F3 cells or transform mouse bone marrow cells but still retains by 30-40% the ability to transform Rat1 cells. Compared with the wild type Bcr-Abl, autophosphorylation of GST/Bcr-Abl-(Delta1-160) in vivo was reduced by more than 50%. The Grb-2 binding to GST/Bcr-Abl-(Delta1-160) was 50% reduced in Rat1 cells and undetectable in Ba/F3 cells. In Rat1 cells expressing GST/Bcr-Abl-(Delta1-160), phosphotyrosine contents of p62 and Shc were 70% decreased.

Adaptor Proteins, Signal Transducing↗

PubMed1996

Analysis of human c-Abl tyrosine kinase activity and regulation in S. pombe.

c-Abl protein tyrosine kinase activity is tightly regulated in vertebrate cells. Several mutations, including deletions of the SH3 domain, can activate abl and convert it into an oncogene. To study c-Abl activity in a cellular environment likely to lack specific regulators, we have expressed human c-Abl in Schizosaccharomyces pombe in an inducible fashion. c-Abl, but not a kinase inactive form of the molecule, causes growth arrest followed by death of the cells. Concomitant to Abl expression we observed extensive phosphorylation of endogenous proteins on tyrosine. Mutations in the SH2 domain or in the autophosphorylation site dramatically reduce the ability of Abl to confer the growth arrest phenotype and to phosphorylate endogenous proteins, suggesting a fundamental role of these structures in the activity of the enzyme. An SH3 domain deletion mutant of Abl is equally active as wild type c-Abl in yeast, even under conditions allowing detection of subtle differences. These results demonstrate that there is no intrinsic regulation of c-Abl kinase activity via the SH3 domain and suggest that the inhibitory effect of the SH3 domain observed in mammalian cells is medicated by a factor that is absent in fission yeast. Expression of Ab1 S.pombe provides a novel quantitative assay for ab1 activity and regulation.

Gene Expression Regulation, Enzymologic↗

PubMed1996

Activation of BTK by a phosphorylation mechanism initiated by SRC family kinases.

Bruton's tyrosine kinase (BTK) is pivotal in B cell activation and development through its participation in the signaling pathways of multiple hematopoietic receptors. The mechanisms controlling BTK activation were studied here by examination of the biochemical consequences of an interaction between BTK and SRC family kinases. This interaction of BTK with SRC kinases transphosphorylated BTK on tyrosine at residue 551, which led to BTK activation. BTK then autophosphorylated at a second site. The same two sites were phosphorylated upon B cell antigen receptor cross-linking. The activated BTK was predominantly membrane-associated, which suggests that BTK integrates distinct receptor signals resulting in SRC kinase activation and BTK membrane targeting.

3T3 Cells↗