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K C Robbins

Publications and source records attributed to K C Robbins.

At least 55 records · Page 3Linked to original sources
PubMed1992

Characterization of the 5' untranslated region of the human c-fgr gene and identification of the major myelomonocytic c-fgr promoter.

In this study, we have characterized the 5' region of the human c-fgr proto-oncogene and identified the major myelomonocytic c-fgr promoter. Seven distinct 5' untranslated exons were identified and localized to a region extending 13 kb upstream from the first coding exon. Two major promoters were identified, one utilized exclusively in Epstein-Barr virus (EBV)-infected B-lymphocyte cell lines, and the other functional only in myelomonocytic cells. Differential promoter utilization and alternative splicing of the 5' untranslated exons give rise to at least six distinct c-fgr mRNA species that differ only in their 5' untranslated regions. Two major mRNAs were identified, c-fgr A and c-fgr 4; these two mRNAs were detected exclusively in EBV-infected B-lymphocyte cell lines and myelomonocytic cells respectively. We have previously demonstrated that c-fgr is transcriptionally activated in U937 cells treated with either 12-O-tetradecanoyl-phorbol-13-acetate (TPA) or cycloheximide (CHX). We now show that a DNA fragment extending from -772 to +97 (with respect to the transcription initiation site upstream from exon M4) is responsive to TPA but not CHX treatment in U937 cells. These results suggest that TPA and CHX induce c-fgr mRNA accumulation by different mechanisms.

Base Sequence↗
PubMed1991

Abnormal plasminogen Maywood I.

Maywood I is a dysfunctional plasminogen. It is described in a patient (W.Y.) with a reduced plasma functional activity and with a low normal antigen level. Plasminogen was isolated from the patients plasma by affinity chromatography with L-lysine-substituted Sepharose. The protein yield was 86 mg/l, which was 88% of the plasma Plg antigen level; the specific activity was 24.4 IU/mg protein compared to 28.5 IU/mg protein for the native molecule. The protein was the Glu-form determined by SDS-PAGE and by isoelectric focusing. Six major isoelectric forms were found with isoelectric points between pH's 6.40 and 5.45. Titration of the equimolar plasminogen.streptokinase complex with p-nitrophenyl-p-guanidinobenzoate gave 85% active-sites indicating a homogenous population of molecules; therefore, the propositus is a homozygote. Four different plasminogen activators: a) streptokinase, b) urokinase c) the plasmin-derived light (B) chain-streptokinase complex, and d) tissue plasminogen activator (with soluble fibrin/CNBr-fibrinogen fragments) generated little plasmin from the variant plasminogen (4.5 to 45 nM), 5% or less than that generated from normal plasminogen. At 45 nM plasminogen, the molar ratio of plasminogen:activator was 3.0 for streptokinase, 3.9 for urokinase, 7.1 for the light (B) chain-streptokinase complex, and 155 for tissue plasminogen activator. In the equimolar variant plasminogen.streptokinase complex, the active-site was slowly developed, to a maximum of 85% in 40 min; in the normal complex, 100% active-sites were developed in 15 min. The variant plasminogen forms two equimolar complexes with streptokinase (I and II), with different mobilities in PAGE, in about equal amounts.(ABSTRACT TRUNCATED AT 250 WORDS)

Electrophoresis, Polyacrylamide Gel↗
PubMed1991

Muscarinic acetylcholine receptor subtypes as agonist-dependent oncogenes.

We have evaluated the muscarinic acetylcholine family of G protein-coupled receptors (mAChRs) for their oncogenic potential. These receptors are preferentially expressed in postmitotic cells, transducing signals specified by their endogenous agonist, the neurotransmitter acetylcholine. Cells transfected with individual human mAChR genes were morphologically indistinguishable from parental NIH 3T3 cells in the absence of agonist. In contrast, when cultures were supplemented with carbachol, a stable analog of acetylcholine, foci of transformation readily appeared in m1, m3, or m5 but not in m2 or m4 mAChRs transfectants. Receptor expression was verified by ligand binding and was similar for each transfected culture. Transformation was dose-dependent and required only low levels of receptor expression. In transformation-competent cells, agonist induced phosphatidylinositol hydrolysis, whereas in m2 or m4 transfectants, receptors were coupled to the inhibition of adenylyl cyclase. These findings demonstrate that mAChRs linked to phosphatidylinositol hydrolysis can act as conditional oncogenes when expressed in cells capable of proliferation.

Adenylyl Cyclase Inhibitors↗
PubMed1991

Differential association of cellular proteins with family protein-tyrosine kinases.

We have sought to identify candidate substrates for src family protein-tyrosine kinases potentially important for transformation. Transfected NIH/3T3 cells, each overexpressing a normal or activated version of the fyn, fgr, or src translational product, were examined using antibody to phosphotyrosine as a probe. Expression of each cDNA induced similar but distinct patterns of tyrosine phosphorylated cellular proteins, with the extent of phosphorylation being greatest in cells expressing an activated kinase. A 70-kDa tyrosine-phosphorylated protein was found to associate with the activated fyn gene product. A protein designated p130, tyrosine phosphorylated in vitro, and in vivo, was found to physically associate with the activated product of each src family gene examined. Physical interaction of three different highly transforming tyrosine kinases with a common cellular protein suggests that p130 may play an important role in transformation induced by src family kinases.

Autoradiography↗
PubMed1991

A novel mechanism regulating growth factor association with the cell surface: identification of a PDGF retention domain.

Platelet-derived growth factor (PDGF) chimeras were used to map a domain responsible for either efficient secretion of PDGF-A or the tight cell association of PDGF-B to their carboxy-terminal domains. Introduction of stop codons within PDGF-A or PDGF-B further dissected their respective carboxy-terminal domains. Although successive deletions of the PDGF-A carboxyl terminus did not impair its secretion, incremental deletions from the carboxyl terminus of PDGF-B abrogated its membrane retention properties and promoted secretion. By this approach, PDGF-B retention properties could be localized to PDGF-B residues 212-226. A processed form of PDGF-B, which contained this domain, was expressed at the cell surface but not released. Comparison of PDGF-B with PDGF-A revealed an analogous sequence located at the PDGF-A carboxyl terminus. We demonstrated that this PDGF-A domain also acts as a retention sequence under conditions that inhibit its proteolytic cleavage. Thus, differences in PDGF-A and PDGF-B secretion relate to differential proteolytic processing of analogous retention domains. All of these findings establish a new mechanism for stable growth factor presentation at the cell surface.

Amino Acid Sequence↗
PubMed1991

A novel c-fgr exon utilized in Epstein-Barr virus-infected B lymphocytes but not in normal monocytes.

The fgr proto-oncogene encodes a nonreceptor protein-tyrosine kinase, designated p55c-fgr. In this study, we have isolated human fgr cDNA molecules from normal monocyte mRNA templates. Nucleotide sequence analysis of the longest fgr cDNA revealed a 5' untranslated region of 927 bp which included two Alu-like repeats as well as three translation stop codons immediately upstream of the initiator for p55c-fgr synthesis. Within genomic DNA, these sequences were distributed over 13 kbp as three distinct 5' untranslated exons. Previous studies have shown that Epstein-Barr virus (EBV) increases c-fgr mRNA levels in B lymphocytes. By comparing the nucleotide sequence reported for transcripts isolated from EBV-infected B lymphocytes with those of our monocyte cDNA as well as genomic DNA, we identified a novel untranslated exon utilized only in EBV-infected cells. The transcriptional initiation sites of fgr mRNA expressed in EBV-converted cells were mapped and shown to reside within a region identified as an intron for fgr mRNA that is expressed in normal myelomonocytic cells. Furthermore, the region of the fgr locus upstream of the novel exon displayed properties of a transcriptional promoter when transfected into heterologous cells. We conclude from all of these findings that activation of the fgr gene by EBV is achieved by mechanisms distinct from those normally regulating its programmed expression in myelomonocytic cells.

B-Lymphocytes↗
PubMed1990

Molecular localization of the transforming and secretory properties of PDGF A and PDGF B.

Human platelet-derived growth factor (PDGF) is a connective tissue cell mitogen comprised of two related chains encoded by distinct genes. The B chain is the homolog of the v-sis oncogene product. Properties that distinguish these ligands include greater transforming potency of the B chain and more efficient secretion of the A chain. By a strategy involving the generation of PDGF A and B chimeras, these properties were mapped to distinct domains of the respective molecules. Increased transforming efficiency segregated with the ability to activate both alpha and beta PDGF receptors. These findings genetically map PDGF B residues 105 to 144 as responsible for conformational alterations critical to beta PDGF receptor interaction and provide a mechanistic basis for the greater transforming potency of the PDGF B chain.

Cell Line, Transformed↗
PubMed1990

Tyrosine phosphorylation coupled to IgE receptor-mediated signal transduction and histamine release.

Antigen-induced cross-linking of IgE bound to its receptors at the surface of basophils or mast cells initiates a number of biochemical events culminating in the release of histamine-containing granules. In the present study, we investigated the possible involvement of tyrosine phosphorylation in signaling by the high-affinity IgE receptor (Fc epsilon RI). Cross-linking of Fc epsilon RI in rat basophilic leukemia cells (RBL-2H3) led to the phosphorylation of several proteins on tyrosine, the most prominent having a mass of 72 kDa. Tyrosine phosphorylation was rapid, detectable 1 min after stimulation, and correlated with both the time course and antigen dose for histamine release. Reversal of Fc epsilon RI cross-linking prevented continuation of the degranulation process and resulted in rapid loss of tyrosine phosphorylation. The receptor-mediated tyrosine phosphorylation was still induced in the absence of calcium in the medium. Depletion of protein kinase C with phorbol 12-myristate 13-acetate did not dramatically affect the tyrosine phosphorylation signal or the release of histamine. In contrast, the calcium ionophore A23187 induced histamine release in the absence of a perceptible increase in protein tyrosine phosphorylation. Thus, tyrosine phosphorylation is an early signal following Fc epsilon RI aggregation, independent of the exocytotic process itself. Taken together, our findings functionally link protein phosphorylation on tyrosine residues to Fc epsilon RI-mediated signal transduction leading to histamine release.

Animals↗
PubMed1990

A small v-sis/platelet-derived growth factor (PDGF) B-protein domain in which subtle conformational changes abrogate PDGF receptor interaction and transforming activity.

Deletion scanning mutagenesis within the transforming region of the v-sis oncogene was used to dissect structure-function relationships. Mutations affecting codons within a domain encoding amino acids 136 through 148 had no effect upon homodimer formation or recognition by antisera which detect determinants dependent upon native intrachain disulfide linkages, yet the same mutations completely abolished transforming activity. A platelet-derived growth factor B (PDGF B) monoclonal antibody that prevents its interaction with PDGF receptors recognized v-sis, delta 142 (deletion of codon 142), and delta 148 but not delta 136, delta 137, or delta 139 mutants. These findings mapped the epitope recognized by this monoclonal antibody to include amino acid residues 136 to 139. Furthermore, mutations in the codon 136 to 148 domain caused markedly impaired ability to induce PDGF receptor tyrosine phosphorylation. Thus, subtle conformational alterations in this small domain critically affect PDGF receptor recognition and/or functional activation.

Animals↗
PubMed1990

Thrombin-dependent association of phosphatidylinositol-3 kinase with p60c-src and p59fyn in human platelets.

Recent studies have shown that ligand-activated growth factor receptors as well as transforming versions of nonreceptor protein-tyrosine kinases physically associate with phosphatidylinositol-3 kinase (PI-3 kinase). Reasoning that PI-3 kinase might also play a role in the normal functions of nonreceptor kinases, we sought to determine whether association with PI-3 kinase might serve as a measure of nonreceptor protein-tyrosine kinase activation under physiological conditions. We found that p60c-src as well as p59fyn, the product of another member of the src family of proto-oncogenes, physically associated with a PI kinase activity within 5 s after exposure to thrombin. Furthermore, PI kinase reaction products generated in p60v-src, p60c-src or p59fyn containing immunoprecipitates were indistinguishable, demonstrating the identity of the associated enzyme as PI-3 kinase. These findings demonstrate a thrombin-dependent interaction between p60c-src or p59fyn and PI-3 kinase and suggest a role for nonreceptor protein-tyrosine kinases in human platelet signal transduction.

Blood Platelets↗
PubMed1990

Chimeric molecules map and dissociate the potent transforming and secretory properties of PDGF A and PDGF B.

Human platelet-derived growth factor (PDGF) is a connective tissue cell mitogen comprising two related chains encoded by distinct genes. The B chain is the homolog of the v-sis oncogene product. Properties that distinguish these ligands include greater transforming potency of the B chain and more efficient secretion of the A chain. By a strategy involving the generation of PDGF A and B chimeras, these properties were mapped to distinct domains of the respective molecules. Increased transforming efficiency segregated with the ability to activate both alpha and beta PDGF receptors. These findings genetically map PDGF B residues 105 to 144 as responsible for conformational alterations critical to beta PDGF receptor interaction, and provide a mechanistic basis for the greater transforming potency of the PDGF B chain.

Animals↗
PubMed1989

Autocrine mechanism for v-sis transformation requires cell surface localization of internally activated growth factor receptors.

v-sis represents a prototype for the class of oncogenes that encode growth factors. Whether its platelet-derived growth factor (PDGF)-like product functionally activates its receptors within the cell or at the cell surface has potential implications in efforts to intervene with the v-sis-transformed phenotype. We demonstrate that intracellular as well as cell surface forms of two PDGF receptor gene products are tyrosine phosphorylated in v-sis transformants. In a chemically defined medium in which cell growth was dependent on v-sis expression, proliferation was partially inhibited by PDGF neutralizing antibody but completely blocked by suramin. Suramin treatment resulted in a marked reduction in tyrosine phosphorylated cell surface PDGF receptors but had no effect on the level of tyrosine phosphorylation of intracellular receptor species. All of these findings demonstrate that the v-sis-encoded mitogen can bind and activate its receptors internally but that activated receptors must achieve a cell surface location in order to functionally couple with intracellular mitogenic signaling pathways.

Animals↗
PubMed1989

Translocation of the FGR protein-tyrosine kinase as a consequence of neutrophil activation.

Recent studies of the FGR protooncogene have shown that expression of its mRNA is limited to mature peripheral blood granulocytes, monocytes, and tissue macrophages. In the present study, we have investigated p55c-fgr expression in normal human neutrophils [polymorphonuclear leukocytes (PMN)] and have found enzymatically active p55c-fgr to be abundant in lysates of PMN and murine fibroblasts transfected with a FGR expression plasmid but not control cells. Fractionation studies revealed that neutrophil p55c-fgr was present in plasma membrane-enriched fractions as well as fractions containing secondary and tertiary granules. Little change in the distribution of p55c-fgr or FGR kinase activity was observed under conditions favoring tertiary granule release. In contrast, when secondary granule secretion was induced with the chemoattractant peptide, formyl-Met-Leu-Phe, a marked decrease in p55c-fgr and FGR kinase was observed in fractions depleted of secondary granules. Concomitantly, the relative concentration of p55c-fgr and its enzymatic activity were increased in fractions containing plasma membrane. From these findings we conclude that p55c-fgr is associated with functional secretory granules and is redistributed within normal neutrophils in response to their activation.

Animals↗
PubMed1989

Expression of the fgr protooncogene product as a function of myelomonocytic cell maturation.

The fgr protooncogene is a member of the src family of protein tyrosine kinases. Recent studies have shown that normal myelomonocytic cells and tissue macrophages are the major sites of fgr mRNA expression. In the present study, we have identified the fgr protooncogene protein product in HL60 cells and have examined its expression as a function of HL60 cell maturation. Whether induced toward monocytic or granulocytic lineages, p55c-fgr accumulated in HL60 cells during maturation. In differentiated cells, the protein was active as a protein tyrosine kinase and was localized to peripheral cell membranes. Demonstration that a myristyl group was covalently bound to the protein probably accounted for its subcellular distribution. These findings establish developmental regulation of p55c-fgr in a lineage that represents its natural site of expression.

Cell Differentiation↗
PubMed1989

The actin domain of Gardner-Rasheed feline sarcoma virus inhibits kinase and transforming activities.

The transforming gene product, P70gag-actin-fgr, of Gardner-Rasheed feline sarcoma virus (GR-FeSV) is a single polypeptide composed of regions derived from cellular and viral genes. Gamma actin and c-fgr genes are the two known cellular components of the GR-FeSV genome. In the present study, sequences representing each cell-derived gene were deleted and the resulting constructs were tested for transforming activity by transfection of NIH 3T3 cells. Constructs lacking a portion of the c-fgr proto-oncogene failed to induce focus formation, demonstrating the essential nature of this component for GR-FeSV oncogenic activity. In contrast, the construct lacking the actin domain was more active than GR-FeSV DNA in transformation assays. Protein specified by the actin deletion mutant possessed a 2.4-fold greater specific protein-tyrosine kinase activity compared with that of the wild-type gene product. Furthermore, the actin domain had no detectable effect on the ability of the fgr kinase to associate with cytoskeleton or to phosphorylate unique cellular proteins on tyrosine. Our findings demonstrate that the actin domain inhibits focus formation and impairs protein-tyrosine kinase activity.

Actins↗
PubMed1989

Association of p60fyn with middle tumor antigen in murine polyomavirus-transformed rat cells.

Rabbit antisera raised against human FYN-specific peptides were used to evaluate the expression of the fyn gene product in normal and murine polyomavirus middle tumor antigen (MTAg)-transformed rat cells. The antisera were capable of detecting p60fyn in both normal and MTAg-transformed cells. Two different antisera directed against unique p60fyn sequences were found to detect p60fyn-MTAg complexes in cell lysates from the MTAg-transformed cells. The MTAg molecules immunoprecipitated by FYN antisera were phosphorylated on tyrosine during immune-complex kinase reactions at sites similar to those found on MTAg in complexes with pp60c-src. Whereas the abundance of p60fyn was estimated to be less in the MTAg-transformed cells than in their normal counterparts, the specific activities of p60fyn molecules in the normal and transformed cells were similar.

Amino Acid Sequence↗