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J R Downing

Publications and source records attributed to J R Downing.

At least 91 records · Page 5Linked to original sources
PubMed1992

PCTAIRE-1 and PCTAIRE-3, two members of a novel cdc2/CDC28-related protein kinase gene family.

We have isolated two murine cDNAs designated PCTAIRE-1 and -3 which encode putative serine/threonine-specific protein kinases. The predicted products of PCTAIRE-1 and -3 are 65% homologous and are organized into a core 295-residue kinase domain flanked by unique 161 and 117 amino acid N-terminal and 40 and 39 amino acid C-terminal domains respectively. The kinase domains are approximately 50-55% homologous to members of the cdc2/CDC28 kinase gene family, and each contains a cysteine-for-serine substitution within the conserved PSTAIRE motif. PCTAIRE-1 was ubiquitously expressed as a predominant 3.0-kb transcript and a minor 2.2-kb mRNA resulting from differential polyadenylation. In contrast, PCTAIRE-3 exhibited a more restricted pattern of expression with a single 3.0-kb mRNA detected in brain, kidney and intestine. The PCTAIRE-1 and -3 products produced by in vitro transcription-translation failed to bind to p13suc1 but were precipitated by antibodies directed to Schizosaccharomyces pombe p34cdc2 or to the human PSTAIRE motif. Thus, PCTAIRE-1 and -3 are members of a novel subfamily of cdc2/CDC28-related protein kinases.

Amino Acid Sequence↗
PubMed1991

Peptide antisera to human colony-stimulating factor 1 receptor detect ligand-induced conformational changes and a binding site for phosphatidylinositol 3-kinase.

A peptide antiserum (anti-A) directed to the intracellular, juxtamembrane region (residues 552 to 574) of the human colony-stimulating factor 1 receptor (CSF-1R) precipitated only ligand-activated, native receptors from solution but bound to unstimulated forms after their denaturation. Two peptide antisera (anti-KI1 and -KI2), directed to residues 679 to 700 and 701 to 721, respectively, in the CSF-1R kinase insert (KI) domain and including mapped sites of ligand-induced phosphorylation at Tyr-699 and Tyr-708, bound at least 80% of the receptor molecules expressed in either CSF-1-stimulated or unstimulated cells. Immune complexes formed with anti-KI1, anti-A, or a peptide antiserum to the CSF-1R carboxyl terminus (anti-C-ter) coprecipitated CSF-1R complexed to a phosphatidylinositol 3-kinase (PtdIns 3-K) from CSF-1-stimulated cells, whereas anti-KI2 serum did not. In an in vitro assay, binding of CSF-1R to PtdIns 3-K required receptor tyrosine phosphorylation but not CSF-1R-mediated phosphorylation of the lipid kinase, and the association was specifically blocked by anti-KI2 or antibodies to phosphotyrosine. Neither anti-KI1, anti-A, nor anti-C-ter serum inhibited binding. We conclude that (i) only a minority of ligand-activated receptors form a stable complex with PtdIns 3-K in vivo, (ii) efficient binding of the lipid kinase requires receptor tyrosine phosphorylation within the CSF-1R KI domain, and (iii) a region within the KI domain defined by residues 701 to 721 at least partially overlaps the PtdIns 3-K binding site.

Amino Acid Sequence↗
PubMed1991

PDGF, CSF-1, and EGF induce tyrosine phosphorylation of p120, a pp60src transformation-associated substrate.

Transformation by activated pp60c-src has been correlated by genetic analysis with the tyrosine phosphorylation of a 120 kilodalton (kDa) protein, p120. We now demonstrate tyrosine phosphorylation of p120 following stimulation of cells by growth factors whose receptors have intrinsic tyrosine-specific protein kinase activity. Stimulation of quiescent NIH3T3 cells with platelet-derived growth factor (PDGF) resulted in the tyrosine phosphorylation of p120 that was maximal by 5 min and returned to background levels by 30 min. p120 was also phosphorylated on tyrosine after addition of colony-stimulating factor 1 (CSF-1) or epidermal growth factor (EGF) to NIH3T3 cells engineered to express high levels of their respective receptors. Two additional src substrates, p110 and p85, were analysed under identical assay conditions. PDGF, CSF-1, and EGF induced only a minimal increase in the tyrosine phosphorylation of p85 and no change in the phosphorylation of p110. Thus, the marked ligand-induced tyrosine phosphorylation of p120 was a property not shared by the other src substrates examined. Immunoblotting with antibodies to p120 and the ras GTPase activating protein, GAP, suggests that p120 and GAP are unrelated. In addition, the amino acid sequences of four cyanogen bromide peptides derived from p120 showed no homology to GAP or to sequences in either the PIR or Swiss-Prot databases. These data suggest that tyrosine phosphorylation of p120 may contribute to both signal transduction through growth factor receptors and pp60src induced transformation.

Amino Acid Sequence↗
PubMed1990

Signal-response coupling mediated by the transduced colony-stimulating factor-1 receptor and its oncogenic fms variants in naive cells.

Colony-stimulating factor-1 (CSF-1 or M-CSF) supports the proliferation and survival of mononuclear phagocytes by binding to a receptor (CSF-1R) encoded by the c-fms proto-oncogene. Whereas the CSF-1R kinase is normally regulated by ligand, receptors bearing 'activating mutations' act constitutively as enzymes and can transform fibroblasts and haemopoietic cells of different lineages. Introduction of human CSF-1R enables mouse NIH-3T3 cells to form colonies in agar in response to human CSF-1 and to proliferate in serum-free medium supplemented with CSF-1, albumin, transferrin and insulin. Similarly, expression of human CSF-1R in interleukin 3-dependent mouse FDC-P1 myeloid cells enables them to grow in CSF-1. High levels of CSF-1R expression in FDC-P1 cells can induce factor-independent growth which is abrogated by a 'neutralizing' monoclonal antibody to the receptor. Therefore, critical mutations in the c-fms gene or overexpression of CSF-1R in immature myeloid precursors might each contribute to leukaemia.

Animals↗
PubMed1990

Structural features of the colony-stimulating factor 1 receptor that affect its association with phosphatidylinositol 3-kinase.

The colony-stimulating factor 1 receptor (CSF-1R), immunoprecipitated with either anti-phosphotyrosine or anti-receptor antibodies from lysates of ligand-stimulated cells, is associated with a phosphatidylinositol (PtdIns) 3-kinase activity. The ligand-independent transforming efficiencies of human CSF-1R mutants containing certain amino acid substitutions at codon 301 in their extracellular domains correlated directly with their levels of associated lipid kinase activity. A tyrosine kinase defective CSF-1R mutant (CSF-1R[met616]), containing a mutated ATP binding site, lacked associated PtdIns 3-kinase activity in immune complexes recovered from CSF-1-stimulated cells. However, CSF-1R[met616] associated with PtdIns 3-kinase when phosphorylated in trans in CSF-1-stimulated cells coexpressing an enzymatically competent CSF-1R tyrosine kinase. Another CSF-1R mutant, (CSF-1R[delta KI]), lacking 67 amino acids from its intracellular 'kinase insert' domain, exhibited a partially impaired ligand-dependent mitogenic response and a significant reduction in its associated PtdIns 3-kinase activity. Ligand-stimulated CSF-1R[delta KI] molecules contained levels of phosphotyrosine almost equivalent to wild-type receptors, but were phosphorylated at different sites in vitro. Therefore, the association of CSF-1R with active PtdIns 3-kinase required the receptor tyrosine kinase activity, was triggered by receptor phosphorylation on tyrosine and, in this series of mutants, correlated with their mitogenic potential. Although the receptor KI domain strongly contributes to the association with PtdIns 3-kinase, this region is not strictly essential for the interaction.

Animals↗
PubMed1990

A point mutation at tyrosine-809 in the human colony-stimulating factor 1 receptor impairs mitogenesis without abrogating tyrosine kinase activity, association with phosphatidylinositol 3-kinase, or induction of c-fos and junB genes.

Substitution of phenylalanine for tyrosine-809 in the human colony-stimulating factor 1 receptor (CSF-1R) inhibited its ability to transduce ligand-dependent mitogenic signals in mouse NIH 3T3 cells. When combined with an "activating" mutation at codon 301 that induces constitutive CSF-1R tyrosine kinase activity, the codon 809 mutation suppressed ligand-independent cell transformation. Comparative mapping of tryptic phosphopeptides from mutant and wild-type CSF-1R indicated that tyrosine-809 is a site of ligand-dependent receptor phosphorylation in vivo. The mutant receptor was active as a tyrosine kinase in vitro and in vivo, underwent CSF-1-dependent association with a phosphatidylinositol 3-kinase, and induced expression of the protooncogenes c-fos and junB, underscoring its ability to trigger some of the known cellular responses to CSF-1. The mutant receptor is likely to be impaired in its ability to interact with critical cellular effectors whose activity is required for mitogenesis.

Animals↗
PubMed1990

Ligand-induced phosphorylation of the colony-stimulating factor 1 receptor can occur through an intermolecular reaction that triggers receptor down modulation.

Ligand-induced tyrosine phosphorylation of the human colony-stimulating factor 1 receptor (CSF-1R) could involve either an intra- or intermolecular mechanism. We therefore examined the ability of a CSF-1R carboxy-terminal truncation mutant to phosphorylate a kinase-defective receptor, CSF-1R[met 616], that contains a methionine-for-lysine substitution at its ATP-binding site. By using an antipeptide serum that specifically reacts with epitopes deleted from the enzymatically competent truncation mutant, cross-phosphorylation of CSF-1R[met 616] on tyrosine was demonstrated, both in immune-complex kinase reactions and in intact cells stimulated with CSF-1. Both in vitro and in vivo, CSF-1R[met 616] was phosphorylated on tryptic peptides identical to those derived from wild-type CSF-1R, suggesting that receptor phosphorylation on tyrosine can proceed via an intermolecular interaction between receptor monomers. When expressed alone, CSF-1R[met 616] did not undergo ligand-induced down modulation, but its phosphorylation in cells coexpressing the kinase-active truncation mutant accelerated its degradation.

Amino Acids↗
PubMed1990

Transforming activities of human CSF-1 receptors with different point mutations at codon 301 in their extracellular domains.

Replacement of leucine 301 in the human colony stimulating factor 1 receptor (CSF-1R) by serine, threonine, glutamic acid, or proline induced ligand-independent transforming activity in mouse NIH3T3 cells, whereas substitution by phenylalanine, methionine, cysteine, or lysine did not. Serine, glutamic acid, and proline mutations were more potent than threonine in inducing cell transformation. The growth of cells transformed by CSF-1R [S301] and [T301] was further stimulated by human recombinant CSF-1, but cells expressing CSF-1R [E301] responded poorly to the growth factor. The transforming efficiency of mutant receptors was also enhanced by the presence of a phenylalanine for tyrosine mutation at codon 969 near the receptor carboxylterminus. Like the v-fms oncogene product, receptors containing S301 or E301 mutations were partially inhibited in their intracellular transport to the plasma membrane, whereas non-transforming variants were transported normally. However, CSF-1R [T301] was processed as efficiently as the wild-type glycoprotein, indicating that the properties of altered transport and cell transformation could be at least partially dissociated. Expression of CSF-1 receptors bearing activating mutations led to increased phosphorylation of cellular substrates on tyrosine, suggesting that cell transformation resulted from constitutive receptor kinase activity. We conclude that only particular mutations at codon 301 mimic an effect of ligand on CSF-1R so as to constitutively activate its growth promoting activity.

Biological Transport↗
PubMed1989

Inhibition of colony-stimulating factor-1 activity by monoclonal antibodies to the human CSF-1 receptor.

Four of 12 monoclonal antibodies (MoAbs) directed to different epitopes in the extracellular domain of the human colony-stimulating factor-1 receptor (CSF-1R, the c-fms proto-oncogene product) specifically inhibit CSF-1 binding to receptor-bearing cells. All four antibodies abrogated CSF-1-dependent colony formation by human bone marrow-derived macrophage precursors and by mouse NIH-3T3 cells expressing a transduced human c-fms gene. In addition, one of these antibodies (designated MoAb 2-4A5) interfered with the ligand-independent proliferation of NIH-3T3 cells transformed by an oncogenic, mutant c-fms allele. Unlike CSF-1 itself, neither MoAb 2-4A5 nor the other three inhibitory antibodies (MoAbs 12-2D6, 12-3A1, and 12-3A3) induced CSF-1R internalization or degradation. These antibodies should prove useful not only for identifying and quantitating CSF-1R on receptor-bearing cells but for abrogating specific receptor signals that govern the proliferation and survival of human mononuclear phagocytes.

Alleles↗
PubMed1989

Phospholipase C-gamma, a substrate for PDGF receptor kinase, is not phosphorylated on tyrosine during the mitogenic response to CSF-1.

Quiescent mouse NIH3T3 cells expressing a transduced human c-fms gene encoding the receptor for colony stimulating factor-1 (CSF-1) were stimulated with mitogenic concentrations of platelet-derived growth factor (PDGF) or CSF-1. Immunoprecipitated phospholipase C-gamma (PLC-gamma) was phosphorylated on tyrosine and calcium was mobilized following treatment of intact cells with PDGF. In contrast, only trace amounts of phosphotyrosine were incorporated into PLC-gamma and no intracellular calcium signal was detected after CSF-1 stimulation. Similarly, CSF-1 treatment did not stimulate phosphorylation of PLC-gamma on tyrosine in a CSF-1-dependent. SV40-immortalized mouse macrophage cell line that expresses high levels of the CSF-1 receptor. In fibroblasts, antiserum to PLC-gamma co-precipitated a fraction of the tyrosine phosphorylated form of the PDGF receptor (PDGF-R) after ligand stimulation, implying that phosphorylated PDGF-R and PLC-gamma were associated in a stable complex. Pre-treatment of cells with orthovanadate also led to tyrosine phosphorylation of PLC-gamma which was significantly enhanced by PDGF, but not by CSF-1. Thus, although the PDGF and CSF-1 receptors are structurally related and appear to be derived from a single ancestor gene, only PDGF-induced mitogenesis in fibroblasts correlated with tyrosine phosphorylation of PLC-gamma.

Animals↗
PubMed1989

Ligand and protein kinase C downmodulate the colony-stimulating factor 1 receptor by independent mechanisms.

The turnover of the colony-stimulating factor 1 receptor (CSF-1R), the c-fms proto-oncogene product, is accelerated by ligand binding or by activators of protein kinase C (PKC), such as the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). The mechanisms of ligand- and TPA-induced downmodulation were shown to differ by the following criteria. First, in cells in which PKC was downmodulated, CSF-1R reexpressed at the cell surface remained sensitive to ligand but was refractory to TPA-induced degradation. Second, a kinase-defective receptor containing a methionine-for-lysine substitution at amino acid 616 at its ATP-binding site failed to undergo ligand-induced downmodulation but remained responsive to TPA. Following CSF-1 stimulation, no intermediates of receptor degradation could be immunoprecipitated with polyvalent antisera to CSF-1R. In contrast, TPA induced specific proteolytic cleavage of the receptor near its transmembrane segment, resulting in the release of the extracellular ligand-binding domain from the cell and the generation of an intracellular fragment containing the kinase domain. Two-dimensional phosphopeptide mapping demonstrated no new sites of phosphorylation in response to TPA in either the residual intact receptor or the intracellular proteolytic fragment. Therefore, PKC appears not to trigger downmodulation by directly phosphorylating the receptor but, rather, activates a protease which recognizes CSF-1R as a substrate.

Cell Line↗
PubMed1988

A point mutation in the extracellular domain of the human CSF-1 receptor (c-fms proto-oncogene product) activates its transforming potential.

A human CSF-1 receptor containing an "activating" mutation in its extracellular domain (serine for leucine 301) induced morphologic transformation, anchorage-independent growth, and tumorigenicity in mouse NIH 3T3 cells. A second regulatory mutation within the receptor's intracytoplasmic carboxy-terminal tail (phenylalanine for tyrosine 969) augmented transforming efficiency but was itself insufficient to induce transformation. Like the v-fms oncogene product, receptors bearing the activating mutation retained high-affinity binding sites for CSF-1 but were retarded in transport to the cell surface and were phosphorylated on tyrosine in the absence of ligand. Although the activating mutation does not affect the CSF-1 binding site in the receptor extracellular domain, it must induce a conformational change that mimics the effect of ligand binding, resulting in CSF-1-independent signals for cell growth.

Animals↗
PubMed1988

Colony-stimulating factor 1-mediated regulation of a chimeric c-fms/v-fms receptor containing the v-fms-encoded tyrosine kinase domain.

A chimeric gene specifying the 308 N-terminal amino acids of the extracellular ligand binding domain of the human c-fms protooncogene joined to the remainder of the feline v-fms oncogene product encodes a functional colony-stimulating factor 1 (CSF-1) receptor. When expressed in mouse NIH 3T3 fibroblasts, the chimeric gene product was rapidly transported to the cell surface, was autophosphorylated on tyrosine only in response to human recombinant CSF-1, underwent ligand-induced but not phorbol ester-induced down-modulation, and stimulated CSF-1-dependent cell proliferation. By contrast, the C-terminally truncated glycoprotein encoded by the v-fms oncogene is partially inhibited in its transport to the plasma membrane, is constitutively phosphorylated on tyrosine, and is relatively refractory to both ligand-induced and phorbol ester-induced down-modulation. Although the v-fms oncogene can transform cells in the absence of CSF-1, its tyrosine kinase activity and turnover can be appropriately regulated by the human c-fms-encoded ligand binding domain. The results confirm that C-terminal truncation of the c-fms gene is insufficient to activate its transforming potential and suggest that an additional mutation in its distal extracellular domain is required for oncogenic activation.

Animals↗
PubMed1988

Ligand-induced tyrosine kinase activity of the colony-stimulating factor 1 receptor in a murine macrophage cell line.

Metabolic labeling of simian virus 40-immortalized murine macrophages with 32Pi and immunoblotting with antibodies to phosphotyrosine demonstrated that the c-fms proto-oncogene product (colony-stimulating factor 1 [CSF-1] receptor) was phosphorylated on tyrosine in vivo and rapidly degraded in response to CSF-1. Stimulation of the CSF-1 receptor also induced immediate phosphorylation of several other cellular proteins on tyrosine. By contrast, the mature cell surface glycoprotein encoded by the v-fms oncogene was phosphorylated on tyrosine in the absence of CSF-1, suggesting that it functions as a ligand-independent kinase.

Animals↗
PubMed1988

A recessive cellular mutation in v-fes-transformed mink cells restores contact inhibition and anchorage-dependent growth.

A contact-inhibited revertant of mink cells transformed by the Gardner-Arnstein strain of feline sarcoma virus was isolated by fluorescence-activated sorting of cells stained with the mitochondria-specific dye rhodamine 123. The revertant cell line exhibited a decrease in its proliferative rate and saturation density and a complete loss of its capacity for anchorage-independent growth, but it remained tumorigenic when inoculated into nude mice. The revertant cells retained a rescuable Gardner-Arnstein feline sarcoma provirus, expressed high levels of the v-fes oncogene product and its associated tyrosine kinase activity, manifested elevated levels of phosphotyrosine-containing cellular proteins similar to those observed in v-fes-transformed cells, and were refractory to retransformation by retroviruses containing the v-fes, v-fms, and v-ras oncogenes. Fusion of the revertant and parental cells generated somatic cell hybrids which formed colonies in semisolid medium, indicating that the block in transformation was recessive. These data together with the observation that the revertant phenotype is unstable in continuous culture suggest that the loss of transformation is due to the presence of limiting quantities of a gene product which functions downstream of the v-fes-coded kinase in the mitogenic pathway.

Animals↗
PubMed1987

Extraction of cellular DNA from human cells and tissues fixed in ethanol.

DNA can be extracted from ethanol-fixed lymphoid cells and tissues. The fixation procedure is simple and rapid, and the DNA extraction itself is the same as that normally used for fresh tissue or cells. DNA extracted from ethanol-fixed material is indistinguishable from DNA extracted from fresh samples based on its purity, its ability to be digested with restriction endonucleases, and its ability to specifically hybridize to DNA probes. The capability to extract DNA from ethanol-fixed cells and tissues eliminates the need for stringent handling and storage requirements of fresh or frozen specimens.

DNA↗
PubMed1987

Analysis of surface antigen profile, TdT expression, and T cell receptor gene rearrangement for maturational staging of leukemic T cells: a pediatric oncology group study.

By using monoclonal antibodies specific for T lineage surface antigens, neoplastic T cells from 53 children with T cell acute lymphoblastic leukemia and T cell non-Hodgkin's lymphoma were analyzed and assigned to phenotypically defined stages of T cell maturation. Cells were also analyzed for T cell antigen receptor beta-chain gene and immunoglobulin heavy and light chain gene rearrangements. Clonal rearrangements of T cell antigen receptor beta-chain gene and a germ-line configuration of the immunoglobulin genes were found in cells from all cases. The expression of the terminal deoxynucleotidyl transferase (TdT) in leukemic T cells was studied by both qualitative immunofluorescence and quantitative enzyme immunoassay, and the level of TdT expression was correlated with maturational stages. Lymphoblasts classified as prethymic (3 patients) did not express detectable TdT. In contrast, cells from approximately 60% of the patients with early (15 patients) or intermediate (19 patients) thymocytic phenotypes and approximately 40% of the patients with mature thymocytic phenotype (16 patients) were positive for TdT. Thus, in these leukemic clones TdT was randomly expressed and showed no correlation with maturational stage.

Antibodies, Monoclonal↗