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 28,634 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Prosomes are small ribonucleoprotein (RNP) particles of unique morphology in the electron microscope but of variable protein and RNA composition, depending on the differentiation state of the cells studied. They were initially observed as subcomplexes of untranslated mRNP. In previous studies, we found that prosomes are associated to the intermediate filaments (IF) of cytokeratin type in HeLa and PtK1 cells. Here we have studied in detail the association of prosomal antigens with the IF networks in PtK1 cells. Contrary to our earlier conclusions, in these cells the vimentin fibers also carry prosomes which, thus, distribute in between the two types of networks. During the selective collapse of the IF induced by acrylamide, and upon recovery after the withdrawal of the drug, no dissociation of the prosome and IF networks of cytokeratin- and vimentin-type could be observed. These data show that even in a dynamic situation, prosome and IF antigens do not dissociate, indicating strongly that they are located on one and the same structure. Furthermore, the differential distribution of specific prosomal antigens between both types of intermediate filament networks indicates that prosomes do not ubiquitously populate the intermediate filaments but occupy subnetworks of either vimentin or cytokeratin type.
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PMID:Specific types of prosomes are associated to subnetworks of the intermediate filaments in PtK1 cells. 128 72

A tumor promoter phorbol 12-myristate 13-acetate (PMA) induces characteristic reversible changes in the cell shape in certain fibroblastic lines. This reaction to PMA may be regarded as a prototype of reorganizations involving formation of stable cytoplasmic processes. Two specific drugs, Taxol and Colcemid, were used to study the role of microtubules and vimentin-containing intermediate filaments (IF) in the development of PMA-induced reorganizations. A short (I h) exposure to PMA induced formation of processes in the control cells rather than in the Colcemid treated cells having depolymerized microtubules and the IF that collapsed around the nucleus. A longer (3-4 h) exposure to PMA of the colcemid-treated cells induced a partial reversal of the IF collapse; those parts of peripheral lamellae that contained IF were transformed into narrow noncontractile processes. It is suggested that the local interaction of the IF with the actin system is an essential step in the formation of processes from lamellae.
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PMID:[The role of intermediate filaments in forming cellular processes induced in fibroblasts by the tumor promoter TPA]. 135 44

To study the interrelationships of endoplasmic reticulum, mitochondria, intermediate filaments, and microtubules, we have developed a quadruple fluorescence labeling procedure to visualize all four structures in the same cell. We applied this approach to study cellular organization in control cells and in cells treated with the microtubule drugs vinblastine or taxol. Endoplasmic reticulum was visualized by staining glutaraldehyde-fixed cells with the dye 3,3'-dihexyloxacarbocyanine iodide. After detergent permeabilization, triple immunofluorescence was carried out to specifically visualize mitochondria, vimentin intermediate filaments, and microtubules. Mitochondria in human fibroblasts were found to be highly elongated tubular structures (lengths up to greater than 50 microns), which in many cases were apparently fused to each other. Mitochondria were always observed to be associated with endoplasmic reticulum, although endoplasmic reticulum also existed independently. Intermediate filament distribution could not completely account for endoplasmic reticulum or mitochondrial distributions. Microtubules, however, always codistributed with these organelles. Microtubule depolymerization in vinblastine treated cells resulted in coaggregation of endoplasmic reticulum and mitochondria, and in the collapse of intermediate filaments. The spatial distributions of organelles compared with intermediate filaments were not identical, indicating that attachment of organelles to intermediate filaments was not responsible for organelle aggregation. Mitochondrial associations with endoplasmic reticulum, on the other hand, were retained, indicating this association was stable regardless of endoplasmic reticulum form or microtubules. In taxol-treated cells, endoplasmic reticulum, mitochondria, and intermediate filaments were all associated with taxol-stabilized microtubule bundles.
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PMID:Interrelationships of endoplasmic reticulum, mitochondria, intermediate filaments, and microtubules--a quadruple fluorescence labeling study. 136 23

Exogenous adenosine diphosphate (ADP), the most potent mitogen for nontransformed African green monkey kidney epithelial cells of the BSC-1 line, rapidly alters the appearance of the cell monolayer. Examination of the cells with indirect immunofluorescence using monoclonal antibodies reveals a considerable reorganization of cytokeratin filaments without a major change in the pattern of microtubules or microfilaments. In untreated confluent cells, cytokeratin filaments are predominantly confined to a star-like spot in the perinuclear area, but these can be seen to begin to spread within 2 min after addition of ADP. The effect is particularly notable using anti-cytokeratin 8 antibodies. At 6 h this process is complete and produces a well-developed filamentous network throughout the cell. By 12 h, the network appears to collapse, so that the filaments again form a spot in the perinuclear area, a process that is complete by 24 h. Immunoblotting of total cellular proteins reveals no apparent alterations in the amounts of several species of cytokeratins, including cytokeratin 8 and 18, at 3 or 24 h after exposure to ADP. Other purine and pyrimidine nucleotides which do not stimulate DNA synthesis in these cells fail to alter cytokeratin organization, and there is no apparent alteration in the distribution of vimentin, another intermediate filament protein. The rapid ADP-induced cytokeratin reorganization appears to coincide with the induction of early growth-response gene transcription in these cells and may be correlated with the capacity of ADP to subsequently initiate DNA synthesis. This dramatic and reversible cytokeratin reorganization immediately after exposure to ADP may be an important step in the mitogenic signal transduction pathway.
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PMID:Cytokeratin reorganization induced by adenosine diphosphate in kidney epithelial cells. 137 34

Nearly all intermediate filament (IF) proteins share two sequence motifs located at the N- and the C-terminal ends of their helical rod domain ('coil 1a' and 'coil 2b', respectively). To examine the structural role of the coil 2b motif, we have performed in vitro assembly studies and in vivo microinjection experiments employing two site-specific reagents: (a) a 20-residue synthetic peptide (C-2) representing the conserved motif itself and (b) a monoclonal antibody (anti-IFA) that recognises an epitope within the conserved coil 2b sequence. We demonstrate here that vimentin protofilaments, when induced to assemble in the presence of C-2 or anti-IFA, show a lower propensity to polymerise and yield various abberant structures. The few filaments that are formed under these conditions appear much shorter than normal IFs and are unravelled or aggregated. Furthermore, when preformed vimentin filaments are exposed to C-2 or anti-IFA, most of the normal IFs are converted into shorter filamentous forms that possess an abberant morphology. None of these effects is seen when vimentin subunits are coincubated with control peptides. Microinjection of anti-IFA into the cytoplasm of interphasic 3T3 cells provokes collapse of vimentin IFs into a juxtanuclear mass and formation of numerous amorphous aggregates distributed throughout the cytoplasm. These two effects are not seen when the anti-IFA is microinjected into the cell nucleus. Our results provide experimental evidence supporting previous suggestions for a role for the conserved coil 2b sequence in filament assembly. We propose that this region is interacting with other sites along the vimentin molecule and that these interactions are essential for proper protofilament-protofilament alignment and filament stability.
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PMID:Involvement of the consensus sequence motif at coil 2b in the assembly and stability of vimentin filaments. 150 Apr 40

alpha B-Crystallin, a major lens protein, is present in clearly detectable amounts in cultured ovarian carcinoma cells. After heat-shock treatment of these cells at 45 degrees C alpha B-crystallin relocalizes from the detergent-soluble, cytosolic fraction to the non-ionic detergent-insoluble nuclear/cytoskeletal fraction. Colchicine treatment of the cells, although giving rise to a vimentin collapse on the nucleus, does not result in redistribution of alpha B-cyrstallin. When this colchicine treatment is followed by heat shock, alpha B-crystallin relocalizes again to the insoluble fraction, indicating that this relocalization is independent of the collapse of the vimentin network.
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PMID:Relocalization of alpha B-crystallin by heat shock in ovarian carcinoma cells. 150 73

The murine keratins Endo B and Endo A, which are homologs of the human keratins K18 and K8, constitute the intermediate filaments (IFs) that are found in all simple epithelia of the adult and in the first epithelial derivatives of the early embryo. The cellular role of simple epithelial keratins in development and differentiation was investigated by inducing filament collapse in HR9 endoderm and F9 embryonal carcinoma cells in which mutant Endo B protein was constitutively expressed. By immunolocalization techniques a perturbation of the keratin network was revealed as well as concomitant disruption of vimentin IFs and displacement of surface desmosomal proteins, demonstrating an intimate structural association of Endo B/A filaments with these cellular components. In aggregates of differentiating F9 cells displaying altered Endo A/B IFs, the formation of a compact, polarized visceral endoderm layer was significantly compromised. These results indicate that an intact keratin network influences the three-dimensional formation of cell-cell or cell-substratum contacts in embryonic visceral endoderm.
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PMID:Disruption of keratin filaments in embryonic epithelial cell types. 171 95

Intermediate filaments in most types of cultured cells coalign with microtubules. Depolymerization of microtubules results in collapse of vimentin and desmin intermediate filaments to the nucleus where they form a perinuclear cap. Collapse can also be induced by microinjection of antibodies against intermediate filament or microtubule proteins. Thus, two filament systems interact with each other. But the molecules mediating this interaction are unknown. One of the candidates for this role is a microtubule motor kinesin. Recent data showed that kinesin is involved in the plus end-directed movement of the membranous organelles along microtubules such as radial extension of lysosomes in macrophages and centrifugal movement of pigment in melanophores. Here we report that injection of the anti-kinesin antibody into human fibroblasts results in the redistribution of intermediate filaments to a tight perinuclear aggregate but had no effect on the distribution of microtubules. Thus, kinesin is involved not only in organelle movement but also in interaction of the two major cytoskeletal systems, intermediate filaments and microtubules.
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PMID:Coalignment of vimentin intermediate filaments with microtubules depends on kinesin. 183 45

Our previous studies of glycosphingolipids (GSLs) of human umbilical vein endothelial cells (HUVECs) established that globoside and ganglioside GM3 are the most abundant GSLs of HUVECs. Both compounds are located intracellularly, as well as on the cell surface. In this study, we demonstrate that the intracellular globoside and GM3 antigens are associated with the vimentin intermediate filaments of the HUVEC cytoskeleton. Immunofluorescence staining of fixed, permeabilized HUVECs showed colocalization of globoside and GM3 with vimentin but not with tubulin or actin. Both GSLs remained associated with intermediate filaments after perinuclear collapse of the filaments induced by colcemid. Indirect evidence that the globoside epitope is present on a GSL is the loss of staining by anti-globoside after methanol fixation and the absence of anti-globoside reactivity with HUVEC proteins on immunoblots. Colocalization of anti-globoside and anti-vimentin was also demonstrated in cryosections of endothelial cells, which indicates that the observed association was not an artifact induced by exposure of cells to detergent or organic solvent. Association of globoside with intermediate filaments was confirmed by immunoelectron microscopy, which demonstrated the presence of antigen along intermediate filaments, as well as on the cell surface and on lipid vesicles. Interferon-gamma decreased the ratio of surface to filamentous globoside staining, but had the opposite effect on GM3 distribution. Less abundant HUVEC GSLs, including Gb3, nLc4, IV2FucnLc4, and IV3NeuAcnLc4, were not detected along filaments. This is the first report of the association of GSLs with intermediate filaments. We suggest that intermediate filaments may play a role in the transport of GSLs.
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PMID:Association of glycosphingolipids with intermediate filaments of human umbilical vein endothelial cells. 189 71

The expression and assembly characteristics of carboxyl- and amino-terminal deletion mutants of rat neurofilament low Mr (NF-L) and neurofilament middle Mr (NF-M) proteins were examined by transient transfection of cultured fibroblasts. Deletion of the carboxyl-terminal tail domain of either protein indicated that this region was not absolutely essential for co-assembly into the endogenous vimentin cytoskeleton. However, deletion into the alpha-helical rod domain resulted in an inability of the mutant proteins to co-assemble with vimentin into filamentous structures. Instead, the mutant proteins appeared to be assembled into unusual tubular-vesicular structures. Additionally, these latter deletions appeared to act as dominant negative mutants which induced the collapse of the endogenous vimentin cytoskeleton as well as the constitutively expressed NF-H and NF-M cytoskeletons in stably transfected cell lines. Thus, an intact alpha-helical rod domain was essential for normal IF co-assembly whereas carboxyl-terminal deletions into this region resulted in dramatic alterations of the existing type III and IV intermediate filament cytoskeletons in vivo. Deletions from the amino-terminal end into the alpha-helical rod region gave different results. With these deletions, the transfected protein was not co-assembled into filaments and the endogenous vimentin IF network was not disrupted, indicating that these deletion mutants are recessive. The dominant negative mutants may provide a novel approach to studying intermediate filament function within living cells.
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PMID:Effects of truncated neurofilament proteins on the endogenous intermediate filaments in transfected fibroblasts. 190 38


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