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P J Owen-Lynch

Publications and source records attributed to P J Owen-Lynch.

At least 19 recordsLinked to original sources
PubMed2006

Role of the C-terminal actin binding domain in BCR/ABL-mediated survival and drug resistance.

Philadelphia chromosome-positive, chronic myeloid leukaemia (CML) stem and progenitor cells have a survival and growth advantage compared with their normal counterparts. The mechanisms through which the BCR/ABL protein tyrosine kinase (PTK) induces these effects and the important domains within this protein are not fully defined. The F- and G-actin binding region of the BCR/ABL C-terminus may be important in BCR/ABL-mediated events, and we have investigated this by expressing a C-terminus deletion mutant of the temperature-sensitive BCR/ABL PTK, in a haemopoietic progenitor cell line, which models the chronic phase of CML. The truncated BCR/ABL PTK displayed similar levels of PTK activity when compared with wild type and activation of second messenger formation (in the form of sn-1,2-diacylglycerol) remains intact. On fibronectin substrata, localisation of the protein to the periphery of the cell was, however, dependent on the C-terminus of BCR/ABL PTK. Deletion of the C-terminus reversed both BCR/ABL-mediated apoptotic suppression and drug resistance although the progenitor cells did retain a proliferative advantage at low concentrations of growth factor. These results demonstrated that the C-terminal actin-binding domain of BCR/ABL is important for some of BCR/ABL PTK-mediated leukaemogenic effects.

Actins↗
PubMed2006

Differential effect of leukaemogenic tyrosine kinases on cell motility is governed by subcellular localisation.

The chemokine, stromal cell-derived factor-1 (SDF-1) is a crucial regulator of stem cell homing and tethering, and potentiation of this pathway in leukaemias may contribute to the pathogenesis of the disease. A key second messenger in SDF-1 signal/response coupling is phosphatidylinositol 3,4,5-triphosphate [PtdIns(3,4,5)P3]. SDF-1 elevated PtdIns(3,4,5)P3 levels markedly in the multipotent FDCP-mix stem cell line. Similarly, transfection with BCR/ABL or TEL/PDGFRbeta leukaemogenic tyrosine kinases chronically elevated PtdIns(3,4,5)P3 levels. However, whilst an SDF-1 chemotactic response was observed in TEL/PDGFRbeta-transfected cells, in BCR/ABL cells this was markedly decreased, which was not due to Ras-pathway activation. Thus, multipotent cells can respond to SDF-1, despite chronic increases in this second messenger indicating that a discrete pool of SDF-1-stimulated PtdIns(3,4,5)P3 production drives the chemotactic response. To discern the mechanism for the differential effects of these oncogenes we considered subcellular localisation. As TEL/PDGFRbeta has a cytosolic location whilst BCR/ABL associates with actin, we removed the actin-binding domain from BCR/ABL. We observed relocation of BCR/ABL to the cytosol and increased SDF-1 responses. We conclude that the localisation of BCR/ABL to the cytoskeleton is essential for effects on motility and moderating SDF-1 responses is not essential in tyrosine kinase-mediated leukaemic transformation.

Actins↗
PubMed2001

Glucose transport regulation by p210 Bcr-Abl in a chronic myeloid leukaemia model.

The regulation of nutrient transport by both cytokines and oncogenes has been linked to haemopoietic cell survival. In this study, we found that activation of Bcr--Abl protein tyrosine kinase was associated with the stimulation of glucose transport in the multipotent haemopoietic cell line FDCP-mix, a cell model for chronic-phase chronic myeloid leukaemia (CML). Bcr--Abl upregulation of glucose transport was mediated by phosphatidylinositol-3-kinase. The observation that Bcr--Abl can regulate glucose transport in a CML cell model raises the possibility that glucose transport regulation may have a role to play in the aberrant survival of stem cells in the chronic phase of CML.

Biological Transport↗
PubMed2000

Bcr-Abl protein tyrosine kinase activity induces a loss of p53 protein that mediates a delay in myeloid differentiation.

Chronic myeloid leukaemia is a haemopoietic stem cell disorder, the hallmark of which is the expression of the Bcr-Abl Protein Tyrosine Kinase (PTK). We have previously reported that activation of a temperature sensitive Bcr-Abl PTK in the multipotent haemopoietic cell line FDCP-Mix for short periods resulted in subtle changes including, a transient suppression of apoptosis and no inhibition of differentiation. In contrast, activation of the Bcr-Abl PTK for 12 weeks results in cells that display a delay in differentiation at the early granulocyte stage. Flow cytometric analysis also indicates that the expression of cell surface differentiation markers and nuclear morphology are uncoupled. Furthermore, a significant number of the mature neutrophils display abnormal morphological features. Prolonged exposure to Bcr-Abl PTK results in interleukin-3 independent growth and decreased p53 protein levels. FDCP-Mix cells expressing a dominant negative p53 and p53null FDCP-Mix cells demonstrate that the reduction in p53 is causally related to the delay in development. Returning the cells to the restrictive temperature restores the p53 protein levels, the growth factor dependence and largely relieves the effects on development. We conclude that prolonged Bcr-Abl PTK activity within multipotent cells results in a reduction of p53 that drives a delayed and abnormal differentiation.

Animals↗
PubMed2000

Role of phosphatidylinositol 3-kinase and specific protein kinase B isoforms in the suppression of apoptosis mediated by the Abelson protein-tyrosine kinase.

Leukemogenic oncogenes, such as the Abelson protein-tyrosine kinases (PTK), disrupt the normal regulation of survival, proliferation, and differentiation in hemopoietic progenitor cells. In the absence of cytokines, hemopoietic progenitor cells die by apoptosis. Abl PTKs mediate suppression of this apoptotic response leading to aberrant survival. To investigate the mechanism of Abl PTK action, we have used an interleukin-3-dependent murine mast cell line that expresses a temperature-sensitive form of the v-ABL PTK, which is active at the permissive temperature of 32 degrees C and inactive at 39 degrees C. At the permissive temperature, these cells are resistant to apoptosis induced both by the withdrawal of the hemopoietic growth factor (interleukin-3) and the addition of cytotoxic drugs. We demonstrate that v-Abl associates with and stimulates activation of phosphatidylinositol 3-kinase (PI3K) and, crucially, that this activation results in enhanced cellular levels of the mass of the second messenger phosphatidylinositol-3,4,5-trisphosphate. Activation of PI3K leads to enhanced activity of PKB and increased levels of the anti-apoptotic protein Bcl-X(L). Transfection of cells with a dominant negative PKB reduces both the Abl-stimulated PKB activity and the survival effect conferred by activation of this oncogene. Thus, PI3K and PKB are required for the anti-apoptotic effects of Abl PTK.

Animals↗
PubMed1998

p210 Bcr-Abl expression in a primitive multipotent haematopoietic cell line models the development of chronic myeloid leukaemia.

Chronic myeloid leukaemia (CML) is a clonal disorder of the pluripotent haemopoietic stem cell, the hallmark of which is the constitutively activated Bcr-Abl protein tyrosine kinase. During the initial chronic phase of CML the primitive multipotent leukaemic progenitor cells remain growth factor dependent and are capable of producing terminally differentiated cells. Although the available evidence suggests that Bcr-Abl directly affects signalling pathways involved in controlling the development of primitive haemopoietic progenitors the identification of the specific biological consequences of Bcr-Abl activity in these progenitors has been hampered by the lack of suitable systems modelling CML. By transfecting the multipotent haemopoietic cell line FDCP-Mix with a temperature sensitive mutant of Bcr-Abl we have developed the first working model that mirrors the chronic phase of CML. FDCP-Mix cells expressing Bcr-Abl tyrosine kinase activity remain growth factor dependent and retain their ability to differentiate. Normal neutrophilic cells are formed in response to G-CSF and GM-CSF. In addition, the transfected FDCP-Mix cells grown at the permissive temperature for Bcr-Abl tyrosine kinase activity display enhanced survival and proliferation in low concentrations of growth factor. These findings are consistent with the initial subtle changes seen in CML progenitor cells during the chronic phase and confirm that Bcr-Abl effects are context specific, i.e. they depend on the origin and developmental potential of the transfected cells. This questions the significance of studies in non-haemopoietic and differentiation blocked haemopoietic cells.

Cell Division↗
PubMed1998

An activated protein kinase C alpha gives a differentiation signal for hematopoietic progenitor cells and mimicks macrophage colony-stimulating factor-stimulated signaling events.

Highly enriched, bipotent, hematopoietic granulocyte macrophage colony-forming cells (GM-CFC) require cytokines for their survival, proliferation, and development. GM-CFC will form neutrophils in the presence of the cytokines stem cell factor and granulocyte colony-stimulating factor, whereas macrophage colony-stimulating factor leads to macrophage formation. Previously, we have shown that the commitment to the macrophage lineage is associated with lipid hydrolysis and translocation of protein kinase C alpha (PKCalpha) to the nucleus. Here we have transfected freshly prepared GM-CFC with a constitutively activated form of PKCalpha, namely PKAC, in which the regulatory domain has been truncated. Greater than 95% of the transfected cells showed over a twofold increase in PKCalpha expression with the protein being located primarily within the nucleus. The expression of PKAC caused macrophage development even in the presence of stimuli that normally promote only neutrophilic development. Thus, M-CSF-stimulated translocation of PKCalpha to the nucleus is a signal associated with macrophage development in primary mammalian hematopoietic progenitor cells, and this signal can be mimicked by ectopic PKAC, which is also expressed in the nucleus.

Animals↗
PubMed1998

Ectopic interleukin-5 receptor expression promotes proliferation without development in a multipotent hematopoietic cell line.

The interleukin-5 (IL-5) receptor is a heterodimer that consists of an IL-5 specific alpha subunit and a common ssc chain that is shared with the receptors for granulocyte macrophage colony stimulating factor (GM-CSF) and interleukin-3 (IL-3). In contrast to IL-5, which acts mainly as an eosinophil lineage specific factor in vivo, IL-3 and GM-CSF stimulate the survival, proliferation and development of various hematopoietic cell lineages and also multipotent progenitor cells. IL-5 has little effect on the survival or proliferation of the multipotent stem cell line FDCP-Mix A4 but does promote some eosinophil development. To investigate whether the lineage specificity of IL-5 is due to the restricted expression of the IL-5 receptor alpha subunit we transfected the FDCP-Mix A4 cells with a retroviral vector containing this alpha subunit. The ectopic expression of the IL-5 receptor alpha subunit in the FDCP-Mix cells did not increase the observed eosinophilic development but did stimulate survival and proliferation of the transfected cells when IL-5 was added. IL-5 thus acts like IL-3 in these cells, promoting proliferation and survival. The results suggest that IL-5, whilst having a capacity to promote proliferation, does not influence eosinophilic lineage commitment in these multipotent cells. The results further argue that the observed lineage specificity of IL-5 is probably due to factors in addition to the restricted expression of the IL-5 receptor alpha subunit.

Animals↗
PubMed1998

Investigation of the molecular mechanisms underlying growth factor synergy: the role of ERK 2 activation in synergy.

Stem Cell Factor (SCF), the ligand for the c-kit proto-oncogene, has been shown to synergistically interact with other cytokines, enhancing the responsiveness of haemopoietic precursors. In this study we have examined the effects of SCF, in combination with interleukin-3 (IL-3), on FDCP-Mix A4 cells, a murine, multipotent, haemopoietic progenitor cell line. Low concentration of IL-3 act to enhance cell survival but do not stimulate proliferation in A4 cells. Similarly, SCF when added alone, acts as a good survival stimulus, but is a poor proliferative stimulus. However, in combination with low concentrations of IL-3, SCF stimulates a synergistic enhancement of proliferation leading to a large increase in cell number after seven days. The synergy observed was not due to SCF stimulated alterations in the mRNA, protein levels or affinity of the IL-3 receptors. Therefore, interactions between cytokines at the level of cytoplasmic signalling pathways were investigated. IL-3 stimulated the rapid and transient tyrosine phosphorylation of several proteins (including those of molecular weights 130, 110, 100, 95, 80, 65, 50 and 45 kDa). Some of these proteins were identified as the Src Homology Collagen (SHC) protein, Janus kinase (JAK-2) and the Mitogen Activated Protein Kinase isoforms ERK 1 and ERK 2. IL-3 also stimulated a transient increase in the activity of both ERK 1 and 2. SCF stimulated a rapid and transient increase in the tyrosine phosphorylation of ERK 1 and ERK 2 although, coaddition of SCF with IL-3, caused no gross differences in the phosphorylation of SHC, JAK-2 or ERKs compared to those observed with IL-3 alone. Coaddition of SCF and low concentration of IL-3 stimulated a reproducible synergistic increase in the activity of ERK 2, whereas only an additive increase in the activity of ERK 1 was observed. These results suggest that ERK 2 activation represents a point at which the two pathways, stimulated by IL-3 and SCF, interact synergistically.

Adaptor Proteins, Signal Transducing↗
PubMed1998

The growth inhibitory role and potential clinical value of macrophage inflammatory protein 1 alpha in myeloid leukaemias.

The control of primitive haemopoietic progenitor cell proliferation in vitro can be achieved with combinations of growth stimulatory cytokines. Acting in apparent opposition to these growth stimulators are growth inhibitory substances, including prostaglandins, cytokines and chemokines which bind to specific cognate cell surface receptors and promote signal transduction events that interfere with cellular proliferation. Within the bone marrow microenvironment, significant quantities of both growth inhibitors and growth promoters can be detected. The ratio of their concentrations within microenvironmental niches of the marrow may regulate primitive blood cell production. The potential exists, therefore, for the disregulation of haemopoiesis via the disruption of the balance between positive and negative regulators of haemopoietic progenitor proliferation. In one particular disease, chronic myeloid leukaemia (CML), there is a lack of response of leukaemic cells to the chemokine growth inhibitor, Macrophage Inflammatory Protein-1alpha (MIP-1alpha). The role of MIP-1alpha in regulation of haemopoiesis, the response of CML progenitor cells and other myeloid leukaemic cells to this chemokine, and the reasons for lack of response to MIP-1alpha in leukaemic cells are reviewed.

Chemokine CCL3↗
PubMed1996

The effect of the chemokine rhMIP-1 alpha, and a non-aggregating variant BB-10010, on blast cells from patients with acute myeloid leukaemia.

The effects of recombinant macrophage inflammatory protein 1 alpha (rhMIP-1 alpha) on the proliferation of leukaemic blast cells from patients with acute myeloid leukaemia was assessed. Using the previously described [3H]thymidine incorporation index assay, the response of autonomous and growth factor responsive AML blast cells to the chemokine rhMIP-1 alpha was measured. In the case of autonomous proliferators, rhMIP-1 alpha had no inhibitory effect on [3H]thymidine incorporation and in 4/6 cases [3H]-thymidine incorporation was stimulated by rhMIP-1 alpha. In the presence of stem cell factor (SCF), a majority (8/9) of the samples which responded to this growth factor were inhibited when rhMIP-1 alpha was included in the assay medium. Similar results were obtained with GM-CSF-responsive samples; however, when these two cytokines were combined, only 3/14 were significantly inhibited. In the presence of human placental conditioned medium (HPCM), rhMIP-1 alpha significantly inhibited [3H]thymidine incorporation in only 2/10 of HPCM-responsive samples. In methylcellulose assays rhMIP-1 alpha had no consistent effect on colony/cluster formation in the presence of either GM-CSF + SCF or HPCM. Similar results were obtained with BB-10010, a mutant of rhMIP-1 alpha which has defined aggregation properties in solution. These data suggest that autonomously proliferating AML cells, and also some AML samples which require cytokines to proliferate, are non-responsive to the growth inhibitors rhMIP-1 alpha and BB-10010 in the presence of multiple growth factors.

Acute Disease↗
PubMed1995

Macrophage inflammatory protein-1 alpha receptors are present on cells enriched for CD34 expression from patients with chronic myeloid leukemia.

The response of normal and chronic myeloid leukemia (CML), CD34+ cells to human macrophage inflammatory protein-1 alpha (MIP-1 alpha or LD78) was assessed. In tritiated thymidine incorporation assays, stem cell factor plus granulocyte-macrophage colony-stimulating factor stimulated thymidine incorporation in normal CD34+ cells was reduced to 72% of control values in the presence of MIP-1 alpha, whereas incorporation by CML CD34+ cells exposed to the same factors was not altered. In clonogenic assays, the presence of MIP-1 alpha gave a level of colony formation that was 71% of control values for normal progenitor cells, whereas for CML CD34+ cells colony formation was enhanced by 25%. These results suggest that, in vitro, CML progenitor cells are relatively refractory to the growth inhibitory effects of MIP-1 alpha. Using flow cytometry, the specific binding of a biotinylated human MIP-1 alpha/avidin fluorescein (FITC) conjugate to normal and CML mononuclear and CD34+ cell populations was quantified. The data indicate that (for both normal and CML CD34+ cells) there was a single population of cells that express cell surface receptors for MIP-1 alpha and this receptor expression was independent of cell cycle status. CML progenitor cells may be refractory to the effects of MIP-1 alpha as a result of events downstream from receptor expression.

Antigens, CD34↗
PubMed1995

v-Abl-mediated apoptotic suppression is associated with SHC phosphorylation without concomitant mitogen-activated protein kinase activation.

A temperature-sensitive mutant of the v-Abl protein has previously been shown to exhibit tyrosine protein kinase activity in Interleukin 3 (IL-3)-dependent IC.DP cells grown at the permissive temperature (32 degrees C) but not at the restrictive temperature (39 degrees C). These IC.DP cells are dependent on IL-3 for suppression of apoptosis at 39 degrees C, but at 32 degrees C cells will survive without added growth factor. Both IL-3 and v-Abl stimulated the tyrosine phosphorylation of SHC and GTPase-activating protein. However, while IL-3 stimulated similar levels of tyrosine phosphorylation in p46shc and p52shc, v-Abl preferentially phosphorylated p52shc, an event that occurred within 1 h of temperature switch. v-Abl also differentially associated with p46shc in a temperature-independent manner. In contrast, only IL-3 stimulated detectable increases in both myelin basic protein kinase and mitogen-activated protein (MAP) kinase kinase in in vitro assays, although in more specific MAP kinase activity assays a very slight increase in the activity of this enzyme was observed after 6 h at the permissive temperature. Time course studies suggest that phosphorylation and association of SHC with v-Abl is insufficient to lead to significant activation of MAP kinase and that activation of the MAP kinase kinase/MAP kinase pathway is not required for apoptotic suppression.

Animals↗
PubMed1995

Suppression of apoptosis by v-ABL protein tyrosine kinase is associated with nuclear translocation and activation of protein kinase C in an interleukin-3-dependent haemopoietic cell line.

We previously demonstrated that activation of v-ABL protein tyrosine kinase resulted in suppression of apoptosis following interleukin-3 removal using an interleukin-3-dependent haemopoietic cell line transfected with a temperature-sensitive mutant of the v-abl oncoprotein (IC.DP). Cellular signalling events associated with the activation of v-ABL included increased levels of sn-1,2-diacylglycerol, an activator of protein kinase C. Calphostin C, a PKC inhibitor, restored apoptosis to interleukin-3-deprived IC.DP cells expressing active v-ABL. However, chronic exposure to the phorbol ester, 12-O-tetradecanoyl phorbol 13-acetate to downregulate protein kinase C did not attenuate the survival of IC.DP cells expressing active v-ABL. Translocation of a classical protein kinase C isozyme(s) to the nuclear fraction was observed 6 hours after activation of v-ABL, when nuclear protein kinase C activity was increased approximately 2-fold. The protein kinase C isozyme responsible, which was only partially downregulated by 12-O-tetradecanoyl phorbol 13-acetate, was identified as protein kinase C beta II. This translocation of protein kinase C beta II to the nucleus was inhibited by calphostin C. Taken together, these results suggest that nuclear translocation and activation of PKC beta II may play a role in v-ABL-mediated suppression of apoptosis.

Animals↗
PubMed1995

Macrophage inflammatory protein-1 alpha mediated growth inhibition in a haemopoietic stem cell line is associated with inositol 1,4,5 triphosphate generation.

Macrophage Inflammatory Protein-1 alpha (MIP-1 alpha) can inhibit the proliferation of multipotent haemopoietic cells. Using the FDCP-Mix A4 multipotent stem cell line, MIP-1 alpha was shown to inhibit 1L-3 stimulated cell cycling (assessed using the [3H]-thymidine "suicide" assay). Furthermore, MIP-1 alpha can inhibit 1L-3-stimulated [3H]-thymidine incorporation in FDCP-Mix cells, with half maximal inhibition observed at 3 ng/ml MIP-1 alpha. Prostaglandin E2, but not MIP-1 alpha was able to elevate cyclic AMP levels in FDCP-Mix A4 cells although both agents can cause growth inhibition. However, MIP-1 alpha addition resulted in a pertussis-toxin-insensitive increase in the level of the second messenger inositol 1,4,5 triphosphate (Ins 1,4,5P3). This response was both rapid (maximal at 5 seconds) and transient. A half maximal effect was observed at 5 ng/ml MIP-1 alpha and the dose dependency correlated with that for MIP-1 alpha mediated growth inhibition. A rapid increase in cytosolic Ca2+ levels was also observed in response to MIP-1 alpha. Inositol lipid hydrolysis and an increase in cytosolic Ca2+ (signals normally associated with proliferation) may therefore be implicated in growth inhibitory mechanisms in multipotent cells.

Animals↗
PubMed1994

Cytokine-mediated protein kinase C activation is a signal for lineage determination in bipotential granulocyte macrophage colony-forming cells.

Granulocyte macrophage colony-forming cells (GM-CFC) have the potential to develop into either macrophages and/or neutrophils. With a highly enriched population of these cells we have found that although GM-CFC are equally responsive to macrophage colony stimulating factor (M-CSF) and stem cell factor (SCF) in terms of DNA synthesis, M-CSF stimulated the development of colonies containing macrophages in soft gel assays, while SCF promoted neutrophilic colony formation. When SCF and M-CSF were combined, mainly macrophage development was stimulated both in soft agar colony-forming assays and liquid cultures. An analysis of some potential signaling mechanisms associated with cytokine-mediated developmental decisions in GM-CFC revealed that M-CSF, but not SCF, was able to chronically stimulate phosphatidylcholine breakdown and diacylglycerol production, indicating that protein kinase C (PKC) may be involved in the action of M-CSF. Furthermore, M-CSF, but not SCF, can increase the levels of PKC alpha (PKC alpha) expression and stimulate the translocation of PKC alpha to the nucleus. When the PKC inhibitor, calphostin C, was added to GM-CFC cultured in M-CSF then predominantly neutrophils were produced, conversely PKC activators added with SCF stimulated macrophage development. The data indicate a role for PKC in M-CSF-stimulated macrophage development from GM-CFC.

Animals↗
PubMed1994

Biological consequences of p160v-abl protein tyrosine kinase activity in a primitive, multipotent haemopoietic cell line.

A temperature sensitive abl protein tyrosine kinase gene was transferred into a multipotent haemopoietic stem cell line, and the primary biological effects of expression of the gene were examined at the permissive and non-permissive temperatures. Unlike previous studies in factor-dependent cell lines, we found that expression of the functional abl protein tyrosine kinase did not lead to growth autonomy. Furthermore, the cells were still able to undergo terminal myeloid differentiation. However, expression of the functional gene did lead to a delay in maturation with a concomitant increase in cell production, had a modest effect in terms of delayed apoptosis particularly when the cells were maintained at a high cell density, and slightly increased the response to sub-optimal concentrations of IL-3. In many respects, therefore, the effects of abl protein tyrosine kinase in these cells mimics the effect of bcr/abl in primary haemopoietic cells where growth factor independence and an aberrant differentiation profile are relatively late events in clonal evolution and are not intermediate consequences of activation of the abl gene.

Apoptosis↗