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  • 1
    Electronic Resource
    Electronic Resource
    Changes in the cytoskeleton of 3T3 fibroblasts induced by the phosphatase inhibitor, calyculin-A (1992)
    Springer
    Journal of muscle research and cell motility 13 (1992), S. 341-353 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Addition of the protein phosphatase inhibitor, calyculin-A, to 3T3 fibroblasts causes a marked change in cell morphology. Initially the cells become rounded, develop surface blebs and then detach from the substratum. In the detached cells an unusual ball-like structure is observed. This study focuses on the cytoskeleton during these calyculin-A-induced morphological changes. Stress fibres disappear as the cells begin to round and aggregates of actin are formed towards the apical surface of the cell. These aggregates condense, in the detached cells, to form the ball structure of approximately 3 μm diameter. Between the ball and the nucleus are cables of intermediate filaments that appear to be attached to the surface of the ball and to the nuclear lamina. Using a procedure designed for the isolation of nuclei the nucleus-ball complex can be obtained. Analysis of the nucleus-ball preparation by immunofluorescence and electron microscopy demonstrate that the ball contains actin and that intermediate filaments are located between the ball and the nucleus. In this preparation, the intermediate filaments also appear to attach to the surfaces of the ball and the nucleus. Electrophoretic analysis of the nucleus-ball preparation indicates that, in addition to actin, a major component of the ball is myosin. It is suggested that the formation of the ball is caused by an actin-myosin-based contractile process, initiated by the phosphorylation of myosin. The aggregation of the actomyosin draws together the intermediate filaments into the area between the ball and nucleus. This hypothesis requires that vimentin binds both to the nucleus and to some component of the ball.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01766462
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  • 2
    Electronic Resource
    Electronic Resource
    Calyculin-A increases the level of protein phosphorylation and changes the shape of 3T3 fibroblasts (1991)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 18 (1991), S. 26-40 
    Details
    ISSN: 0886-1544
    Keywords: vimentin ; phosphatase inhibitors ; intermediate filaments ; stress fibers ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Calyculin-A, an inhibitor of type 1 and 2A phosphatases, was applied extracel-lularly to 3T3 fibroblasts. At 0.1 μM, calyculin-A caused a marked increase in protein phosphorylation in both the cytosolic and insoluble cellular fractions. This effect was independent of external Ca2+. An immunoprecipitate, formed with an antibody to myosin, contained several cytoskeletal components. Increased phos-phorylation following treatment with calyculin-A was observed in vimentin, the 20-kD myosin light chain, and an unidentified 440-kD component. An enhanced level of vimentin phosphorylation was found in intermediate filament preparations from treated cells.Calyculin-A also caused marked shape changes of 3T3 cells. Within minutes after addition of calyculin-A (0.1 μM) cells became rounded and lost attachment to the substratum. Stress fibers, intermediate filaments, and microtubules, prominent in the attached control cells, were not evident in the rounded cells. Shape changes were reversible and after removal of calyculin-A the rounded cells attached to the substratum, resumed a flattened shape, and were active mitotically. In the cells treated with calyculin-A an unusual “ball-like” structure was observed with transmission electron microscopy. This unique structure was 2-3 μM in diameter and was located close to the nucleus.The use of calyculin-A adds further support to the idea that cell shape is controlled, at least in part, by concerted actions of a kinase-phosphatase couple.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970180104
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    Paper (German National Licenses)
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