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  • 1
    Electronic Resource
    Electronic Resource
    Stimulation of lymphocyte receptor capping by the ionophore monensin (1983)
    Springer
    The journal of membrane biology 73 (1983), S. 91-93 
    Details
    ISSN: 1432-1424
    Keywords: receptor ; capping ; monensin ; Na+ ; Ca2+ ; contractile machinery
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The carboxylic ionophore monensin has a biphasic effect on antibody-induced Thy-1 cap formation. At higher concentrations, 5×10−6−5×10−5 m monensin causes a significant inhibition of receptor capping similar to that previously found with the Ca2+ selective ionophore A23187. At lower concentrations, 5×10−8−5×10−7 m capping is stimulated. It is concluded that capping at lower ionophore concentrations is a secific response to the ability of monensin to induce a rise in intracellular Na+, which indirectly elevates intracellular Ca2+ activity. This in turn activates the contractile machinery required for the aggregation of surface receptors into capped structures. At higher concentrations monensin acts as a nonspecific detergent, which causes detrimental structural alterations in some of the membrane components involved in the capping process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870343
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  • 2
    Electronic Resource
    Electronic Resource
    Receptor capping in mouse T-lymphoma cells: A Ca2+ and calmodulin-stimulated ATP-dependent process (1983)
    Springer
    The journal of membrane biology 75 (1983), S. 65-72 
    Details
    ISSN: 1432-1424
    Keywords: T-lymphoma cells ; capping ; calmodulin ; Ca2+ ; concanavalin A ; ATP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary The roles that Ca2+, calmodulin, and ATP play in the redistribution of conconavalin A (Con A) binding sites on the surface of mouse T-lymphoma cells were examined. Membranes of cells labeled with fluorescein-conjugated Con A (Fl-Con A) were made permeable (“skinned”) to ions and proteins by incubation in a solution containing no added Ca2+, 7mm EGTA, and ATP. The intracellular ionic and protein concentrations could then be varied, and the degree of Con A receptor capping monitored simultaneously. A graded increase (9.0 to 30%) was found in the number of capped cells with increasing Ca2+ concentration from 10−6–10−4.9 m. Increasing concentrations of trifluoperazine, chlorpromazine, and promethazine (1.5×10−6 to 1.0×10−4 m) in cell suspensions containing 10−4 m Ca2+ produced graded inhibition of capping in the same order that the drugs bind to calmodulin. Removal of extracellular Ca2+ dissociated (reversed) some of the caps into patches, thus reducing their number (12%). ATP was required for either capping or cap dissociation to occur. Addition of calmodulin (3.9×10−8–6.3×10−7 m) to the cell suspension increased the Ca2+ sensitivity. These results provide direct evidence that capping of Con A receptors is a reversible process (i) regulated by intracellular Ca2+ concentration, (ii) requiring ATP as an energy source, and (iii) susceptible to the influence of calmodulin. These findings are consistent with the hypothesis that the collection of surface receptor patches into cap structures is controlled by the interaction of actomyosin filaments, which in turn is regulated by a Ca2+-calmodulin-activated control system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01870800
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  • 3
    Electronic Resource
    Electronic Resource
    Capping of concanavalin a receptors and their association with microfilaments in monolayer grown human fibroblastoid cells (1980)
    Springer
    Cell & tissue research 205 (1980), S. 77-84 
    Details
    ISSN: 1432-0878
    Keywords: ConA capping ; Microfilaments ; Fibroblastoid cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The distribution of ConA binding sites on the surface of normal human fibroblastoid cells grown in monolayer culture was carefully examined. Low concentrations of ConA (between 0.5–5.0 μg/ml) were found to induce the ConA receptors to form a single, large cap structure. High concentrations of ConA (between 50–100 μg/ml) inhibit cap formation at temperatures above 20° C. Pretreatment of the cells in the cold or with colchicine allows cap formation to occur with high concentrations of ConA. The ConA caps appear to be preferentially localized near the nucleus. Using a double immunofluorescence technique, we have observed actin and myosin molecules concentrated underneath the surface receptor cap in the perinuclear region of the cells. These findings suggest that the binding of ConA to fibroblastoid cells may trigger the transmembrane association of cytoplasmic microfilaments with surface membrane receptors as previously proposed for lymphocytes and other round cells grown in suspension culture.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00234444
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  • 4
    Electronic Resource
    Electronic Resource
    Lymphocyte activation and capping of hormone receptors (1988)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 37 (1988), S. 131-150 
    Details
    ISSN: 0730-2312
    Keywords: hormone-receptor interaction ; hormone receptor exposure ; receptor patching/capping ; contractile proteins ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: In this study both a Ligand-dependent treatment [concanavalin A (Con A)] and a ligand-independent treatment [high-voltage pulsed galvanic stimulation (HVPGS)] have been used to initiate lymphocyte activation via a transmembrane signaling process. Our results show that both treatments cause the exposure of two different hormone [insulin and interIeukin-2 (IL-2)] receptors within the first 5 min of stimulation. When either insulin or IL-2 is present in the culture medium, the stimulated lymphocytes undergo the following responses: (1) increased free intra-cellular Ca2+ activity; (2) aggregation of insulin or IL-2 receptors into patch/cap structures; (3) tyrosine-kinase-specific phosphorylation of a 32-kd membrane protein; and finally (4) induction of DNA synthesis.Further analysis indicates that hormone receptor capping is inhibited by (1) cytochalasin D, suggesting the involvement of microfilaments; (2) sodium azide, indicating a requirement for ATP production; and (3) W-5, W-7, and W-12 drugs, implying a need for Ca2 + /calmodulin activity. Treatment with these metabolic or cytoskeletal inhibitors also prevents both the tyrosine-kinase-specific protein phosphorylation and DNA synthesis which normally follow hormone receptor capping. Double immunofluorescence staining shows that actomyosin, Ca2+/calmodulin, and myosin light-chain kinase are all closely associated with the insulin and IL-2 receptor cap structures.These findings strongly suggest that an actomyosin-mediated contractile system (regulated by Ca2+, calmodulin, and myosin light-chain kinase in an energy-dependent manner) is required not only for the collection of insulin and IL-2 receptors into patch and cap structures but also for the subsequent activation of tyrosine kinase and the initiation of DNA synthesis. We, therefore, propose that the exposure and subsequent patching/capping of at least one hormone receptor are required for the activation of mouse splenic T-Iymphocytes.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240370202
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  • 5
    Electronic Resource
    Electronic Resource
    Phosphorylation of a tropomyosin-like (30 KD) protein during platelet activation (1985)
    New York, N.Y. : Wiley-Blackwell
    Journal of Cellular Biochemistry 29 (1985), S. 19-30 
    Details
    ISSN: 0730-2312
    Keywords: phosphorylation ; tropomyosin ; phorbol esters ; platelet activation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: In this study, we have used the tumor promoter 12-o-tetradecanoylphorbol-13-acetate (TPA), as well as its biologically inactive analogue 4α-phorbol 12, 13-didecanoate (4α-PDD), to investigate platelet protein phosphorylation and its possible correlation with platelet activation. Our data show that TPA, but not 4α-PDD, induces a preferential phosphorylation of a 30,000 dalton (30 KD) protein. This phosphoprotein is found to be physically associated with an actomyosin-containing platelet cytoskeleton complex. Further analysis using both standard two-dimensional gel electrophoresis and one-dimensional urea-SDS gel electrophoresis reveals that this 30 KD protein has several tropomyosin-like properties. Most importantly, the degree of TPA-induced phosphorylation of the 30 KD protein is directly proportional to the extent of platelet granule release and the shape change of the platelet, as well as to the degree of aggregation. We speculate that this phosphorylated tropomyosinlike protein may play a pivotal role in the regulation of actomyosin-mediated platelet contractility, which has been previously implicated in a variety of platelet functions.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcb.240290103
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  • 6
    Electronic Resource
    Electronic Resource
    Endocytosis of mannose-6-phosphate binding sites by mouse T-lymphoma cells (1986)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 127 (1986), S. 146-161 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The endocytosis and intracellular transport of mannose-6-phosphate conjugated to bovine serum albumin (Man-6-P:BSA) by mouse T-lymphoma cells were investigated in detail using several methods of analysis, both morphological and biochemical. Man-6-P:BSA was labeled with fluorescein or 125I and used to locate both surface and intracellular Man-6-P binding sites by light or electron microscopy, respectively. Incubation of cells with either fluorescent or 125I-labeled Man-6-P:BSA at 0°C revealed a uniform distribution of the Man-6-P binding sites over the cell surface. Competition experiments indicate that the Man-6-P:BSA binding sites on the cell surface are the same receptors that can recognize lysosomal hydrolases. After as little as 1 min incubation at 37°C, endocytosis of Man-6-P binding sites was clearly observed to occur through regions of the plasma membrane and via vesicles that also bound anticlathrin antibody. After a 5-15-min incubation of cells at 37°C, the internalized ligand was detected first in the cis region of the Golgi apparatus and then in the Golgi stacks using both autoradiography and immunocytochemistry to visualize the ligand. The appearance of Man-6-P:BSA in the Golgi region after 15-30 min was confirmed by subcellular fractionation, which demonstrated an accumulation of Man-6-P:BSA in light membrane fractions that corresponded with the Golgi fractions. After a 30-min incubation at 37°C, the internalized Man-6-P binding sites were localized primarily in lysosomal structures whose membrane but not lumen co-stained for acid phosphatase. These results demonstrate a temporal participation of clathrin-containing coated vesicles during the initial endocytosis of Man-6-P binding sites and that one step in the Man-6-P:BSA transport pathway between plasma membrane and the lysosomal structure can involve a transit through the Golgi stacks.
    Additional Material: 15 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041270118
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  • 7
    Electronic Resource
    Electronic Resource
    The capping of lymphocytes and other cells, studied by an improved method for immunofluorescence staining of frozen sections (1978)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 95 (1978), S. 239-257 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Experiments have been carried out on the capping by lectins and antibodies of surface receptors of mouse splenic T and B lymphocytes and other cells, in which the surface distribution of the lectin or antibody, and the intracellular distribution of myosin or actin, were determined on the same cells by a double fluorescence technique. For this purpose, a general method for intracellular staining was developed which is intended to preserve sensitive antigens and fragile ultrastructural elements. The method involves mild formaldehyde fixation of the cells or tissues, infusion with concentrated sucrose, rapid freezing, and the preparation of frozen sections thinner than 2 μm thickness. The immunofluorescent or other appropriate fluorescent reagents are then applied to the thawed section. In the present experiments, intracellular actin was detected using a fluorescent staining method based on the interaction of F-actin with heavy meromyosin, while intracellular myosin was detected by an indirect immunofluorescence procedure. Our findings were that the formation of a cap by each of the lectins or antibody reagents was always accompanied by a concentration of myosin and actin directly under the cap. These and other results suggest that capping is an active process in which actin and myosin participate directly in the formation of all caps. This proposal carries important new implications for the molecular mechanism of capping.
    Additional Material: 1 Tab.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1040950302
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  • 8
    Electronic Resource
    Electronic Resource
    Rapid separation of mouse T and B lymphocytes using wheat germ agglutinin (1979)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 99 (1979), S. 95-99 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A separation procedure has been developed for mouse splenic T and B lymphocytes which is based on their differential agglutination by wheat germ agglutinin (WGA). In the presence of 50-100 μg/ml of WGA, multicellular aggregates are formed which are enriched in B cells. These aggregates can be separated from monodisperse T cells by gravity sedimentation and subsequently dissociated into single cells by treatment with N-acetylglucosamine (NAG). Immunocytochemical analyses and mitogenic assays indicate approximately 10-15% cross contamination of the resultant B and T cell fractions. The separation procedure is not only convenient and rapid but also allows the simultaneous recovery of viable T and B cells from the same spleen preparation.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1040990111
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  • 9
    Electronic Resource
    Electronic Resource
    Intracellular localization of certain membrane glycoproteins in mouse T-lymphoma cells using immunoferrtin staining of ultrathin frozen sections (1982)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 110 (1982), S. 203-212 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Comparative studies on the cellular morphology of cultured mouse T-lymphoma cells (with particular emphasis on organelles and membrane-associated materials) were conducted using both frozen thin sections and epon thin sections. Due to the fact that the frozen thin sectioning technique allows antigenicity to be retained and also permits good accessbility of the external macromolecular reagents to the interior of the cell, we have been able to explore the intracellular localization of some membrane glycoproteins such as Con A-binding sites and viral membrane glycoprotein, gp 69/71. Our data indicate that most of the membranous cellular structures (e.g., rough endoplamic reticulum, vesicles, Golgi and nuclear envelope) contain the Con A-specific sugars, mannose, and glucose. In addition, we have found that intracellular gp 69/71 molecules exist in an aggregated form at the terminal region of cisternae of rough endoplasmic reticulum and in vesicles of two size ranges (0.1 to 0.15 μ and 0.3 to 0.4μm) as wells as in the cytoplasm close to the plasma membrane. These findings have not only confirmed close some of the previous biochemical data but have also provided new information concening the biochemical nature of intracellular membrane components and the possible biosynthetic fate of membrane precursor molecules.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041100215
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  • 10
    Electronic Resource
    Electronic Resource
    Lymphocyte capping induced by polycationized ferritin (1980)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Cellular Physiology 105 (1980), S. 7-15 
    Details
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In order to better understand the mechanism of lymphocyte surface receptor redistribution induced by externally added ligands, polycationized ferritin (PCF), a nonconventional ligand, was tested using both fluorescence and electron microscopy for its ability to cause patching and capping of anionic molecules on the surface of both transformed and normal mouse lymphocytes. Binding of PCF at 0°C for 1 hour induces the appearance of patches; subsequent incubation at 37° for 30-60 minutes causes the formation of a cap structure with the lymphoid cells tested (T-lymphoma cells and splenic lymphocytes). Using various experimental treatments (e.g., sodium azide, cytochalasin B and D, colchicine, prefixation, and cold temperatures), PCF-induced capping has been found to be temperature sensitive, and to require metabolic energy and an intact cytoskeletal system. In addition, using double immunofluorescence techniques which involve rhodamine-labeled PCF and fluorescein-conjugated heavy meromyosin, it has been observed that the formation of the PCF-induced cap coincides with an accumulation of intracellular actin directly beneath the cap structure. Furthermore, agents such as dibutyryl cyclic AMP and theophylline, which cause an increase in intracellular cyclic AMP, have been shown to stimulate PCF-associated capping. This study suggests that increasing levels of intracellular cyclic AMP may activate, directly or indirectly, membrane-associated contractile elements required for the aggregation of membrane proteins into patches and caps.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jcp.1041050103
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