The effects of naproxen sodium on specific parameters of L-strain cells over guided bone regeneration barrier materials

There is strong evidence that nonsteroidal antiinflammatory drugs (NSAID) may exert a significant antiproliferative effect. This study evaluated the influence of NSAID on specific parameters of fibroblastic cells, in vitro, over two-guided bone regeneration (GBR) barrier materials. Fibroblast cells were cultured on bioabsorbable membrane made of collagen (Bio-Gide(R)- BG) and the most common nonresorbable membrane which is made of expanded polytetrafluoroethylene (ePTFE, Gore-Tex(R)- GT). Naproxen sodium (10 mM) was used as an analgesic drug. The fibroblast cells were cultured in vitro for 24 h and examined by scanning electron microscopy (SEM). Cells were cultured in the presence of (3)H-thymidine to study cell proliferation. And also cell numbers and viabilities were measured. The difference between the means for each group were analyzed for statistical significance by Kruskal-Wallis one-way ANOVA followed by post hoc comparisons using the Dunn statistical method. Of all the six groups, the control group stimulated DNA synthesis more than the others. With respect to cell numbers, there was statistically significant difference between the control group and naproxen planted BG membrane group. The interpretation of our SEM images is that these two barriers and naproxen seem to have had the least effect on cellular morphology. These data suggest naproxen have an inhibitory effect on stimulation of DNA synthesis, cell numbers and viabilities. And also lacking adherence of cells to the membranes may be due to the physical properties of the materials.

The morphogenesis of herpes simplex virus type 1 in infected parental mouse L fibroblasts and mutant gro29 cells

Mutants of cell lines and viruses are important biological tools. The pathway of herpesvirus particle maturation and egress are contentious issues. The mutant gro29 line of mouse L cells is defective for egress of herpes simplex virus type 1 (HSV-1) virions, and a candidate for studies of virus-cell interactions. The properties of uninfected and HSV-1-infected L fibroblasts and gro29 cells investigated by protein assay, immunoblot, titration assay, immunofluorescence light microscopy and immunogold cryosection electron microscopy are reported. The ultrastructure of both HSV-1-infected L and gro29 cells confirmed primary envelopment of virions at the nuclear membranes followed by maturing multiple de-envelopments and re-envelopments in the endoplasmic reticulum and in the Golgi complex. The gro29 cells presented changed cytoskeleton, abolished egress of virions, and were defective in the trafficking of glycoproteins, giving rise to accumulation of viral particles and glycoproteins in the endoplasmic reticulum and the Golgi complex. The results suggest that gro29 cells harbour a causal underlying defect of the cytoskeleton in addition to the HSV-1-induced cytoskeletal changes.

In vitro cellular accumulation of gadolinium incorporated into chitosan nanoparticles designed for neutron-capture therapy of cancer

The accumulation of gadolinium loaded as gadopentetic acid (Gd-DTPA) in chitosan nanoparticles (Gd-nanoCPs), which were designed for gadolinium neutron-capture therapy (Gd-NCT) for cancer, was evaluated in vitro in cultured cells. Using L929 fibroblast cells, the Gd accumulation for 12 h at 37 degrees C was investigated at Gd concentrations lower than 40 ppm. The accumulation leveled above 20 ppm and reached 18.0+/-2.7 (mean+/-S.D.) microg Gd/10(6) cells at 40 ppm. Furthermore, the corresponding accumulations in B16F10 melanoma cells and SCC-VII squamous cell carcinoma, which were used in the previous Gd-NCT trials in vivo, were 27.1+/-2.9 and 59.8+/-9.8 microg Gd/10(6) cells, respectively, hence explaining the superior growth-suppression in the in vivo trials using SCC-VII cells. The accumulation of Gd-nanoCPs in these cells was 100-200 times higher in comparison to dimeglumine gadopentetate aqueous solution (Magnevist), a magnetic resonance imaging contrast agent. The endocytic uptake of Gd-nanoCPs, strongly holding Gd-DTPA, was suggested from transmission electron microscopy and comparative studies at 4 degrees C and with the solution system. These findings indicated that Gd-nanoCPs had a high affinity to the cells, probably contributing to the long retention of Gd in tumor tissue and leading to the significant suppression of tumor growth in the in vivo studies that were previously reported.

Characteristic biological effects of itraconazole on L929 fibroblasts and their cell membrane

Itraconazole (ITCZ), a triazole antifungal agent, was studied for its effects on the morphology and function of L929 fibroblasts. L929 fibroblasts were cultured for 20 h with ITCZ or one of several other triazoles (fluconazole, ketoconazole, and hydroxy-itraconazole [ITCZ-OH]) at the concentration of 0.5 microg/ml. Among these agents, only ITCZ and its metabolite ITCZ-OH markedly elongated the cells bidirectionally. Scanning electron microscopy studies showed that the surface of the elongated cells was smoother than that of the untreated cells. The viability of L929 cells cultured with 0.5 microg/ml of ITCZ for 20 h was not lowered. However, after treatment with 0.0375% sodium deoxycholate (DOC) solution, the viability of the cells treated with ITCZ, as evaluated by the 3-(4,5-dimethyl-2thiazoyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) proliferation assay or the release of lactic dehydrogenase from cytoplasm, was decreased. When L929 cells were cultured in the presence of a combination of ITCZ and vincristine, their growth was synergistically inhibited. This synergism was also observed when ITCZ was replaced by ITCZ-OH, but not by the other azoles. These findings suggest that the exposure of L929 fibroblasts to low ITCZ concentrations affects the physiological nature of their cell membrane.

Neurite formation induced in neuroblastoma cells and genetically altered non-neuronal cells

Ultrastructural changes associated with neurite formation were examined in suitably cultured neuroblastoma cells (Neuro-2a) and drebrin (developmentally regulated brain protein) gene-transfected fibroblasts (L cells) in culture. Both neuroblastoma cells and fibroblasts initially were flattened and epitheloid, with many microspikes or microvilli diffusely distributed over their surfaces. Intracellular organelles were abundant and diffusely arranged. In the transformed state, both cell types were round to oval with long processes where microspikes were concentrated. A constant arrangement of surface and intracellular structures was apparent, though drebrin gene-transfected fibroblasts retained some of their original characteristics. Neurite formation programmed by genes may be initiated by environmental factors in neuroblastoma cells. Neurite-like processes in fibroblasts may be formed due to changes in microfilaments resulting from transfection of the drebrin (actin-binding protein) gene.

Scanning electron microscopy of C-banding

The mechanism of C-banding was analyzed on the basis of the structural changes of the 30 nm chromatin fibre using scanning electron microscopy (SEM). SEM of non-banded metaphase spreads of L-cells revealed chromosomes consisting of 30 nm chromatin fibre loops along the entire length. No marked difference in both the dimension and appearance of such looped structures was discernible between the centromeric region and the rest of the chromosome. In contrast, C-banded chromosomes exhibited a conspicuous alteration of the fibre conformation in the centromeric region. The looped, fibrous structures were almost completely lost from this region, while the non-centromeric region still exhibited fibrous structures with slightly different appearances compared with those observed in the control chromosomes. On the other hand, results obtained using fluorescence microscopy showed that more DNA retained in the centromeric region than in the non-centromeric region. Since the analytical experiments exhibited that the characteristic collapsed state of the centromeric region occurred only with the alkali treatment but neither with the 2 x SSC nor acid treatments, the centromeric heterochromatin seemed to contain some specific protein which should be sensitive to alkali. The structurally collapsed but subsequently compact centromeric region may become more, or still, resistant to the DNA extraction due to the 2 x SSC treatment and the centromeric chromatin thus retained may be visualized as the C-band.

The 59 kDa FK506-binding protein, a 90 kDa heat shock protein binding immunophilin (FKBP59-HBI), is associated with the nucleus, the cytoskeleton and mitotic apparatus

FKBP59-HBI, a 59 kDa FK506 binding protein which binds the 90 kDa heat shock protein hsp90 and thus is a heat shock protein binding immunophilin (HBI), was originally discovered in association with unliganded steroid receptors in their heat shock protein containing heterooligomer form. It belongs to a growing family including other FKBPs which bind the immunosuppressants FK506 and rapamycin, and cyclophilins which bind cyclosporin A, all having rotamase (peptidyl-prolyl cis-trans isomerase) activity which may be involved in protein folding. Targets for drug-immunophilin complexes have been mostly studied in vivo in T lymphocytes; however, immunophilins are present in all cell types, where their role and distribution are still unknown. Here we report the localization of FKBP59-HBI in various non lymphoid cells (mouse fibroblasts (L-929), monkey kidney cells (Cos-7), Madin-Darby canine kidney epithelial cells (MDCK), and mouse neuronal cells (GT1)). Two polyclonal antipeptide antibodies directed against the C-terminal end (amino acids 441–458) (Ab 173) or the sequence 182–201 (Ab 790) of the FKBP59-HBI were used in light and confocal laser immunofluorescence. FKBP59-HBI was found in the cytoplasm and nucleus of interphase cells. Specific immunofluorescence was much stronger in the cytoplasm than in the nucleus when using Ab 173, and stronger in the nucleus than in the cytoplasm with Ab 790. Detailed observations of L-cells, which have a particularly flat morphology, showed a punctate as well as a fibrous cytoskeletal staining in the cytoplasm using antibody 173, a result which suggests interactions of FKBP59-HBI with an organized network. Colocalization experiments (using antibodies against tubulin, vimentin or actin) and use of cytoskeletal-disrupting drugs revealed partial association of FKBP59-HBI with the microtubules. Western blot experiments confirmed that the protein was present in the subcellular fractions containing either ‘soluble’ proteins released from cells exposed to NP40 detergent, or proteins released from the cytoskeleton exposed to calcium ions (i.e. in microtubule depolymerizing conditions). Exposure of cells to 1 microM FK506 and rapamycin for 1 hour did not modify significantly the staining, although rapamycin treatment rendered the network stained by 173 clearly visible. Interestingly, during mitosis FKBP59-HBI segregated from the region of the chromosomes; it mainly localized with the mitotic apparatus (centrosome, spindle and interzone separating the chromosomes), the cleavage furrow and the midbodies during cytokinesis. It appeared again as a fibrous network in the cytoplasm of the two daughters cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Combination of the chemotherapeutic agent 5-fluorouracil with an inhibitor of its catabolism results in increased micronucleus induction

The rate limiting step in 5-fluorouracil catabolism is catalyzed by the enzyme dihydropyrimidine dehydrogenase. Since degradation of 5-fluorouracil decreases its efficacy in chemotherapy, the inhibition of its catabolism is a promising tool. We investigated the formation of micronuclei in vitro in mouse L5178Y cells. 5-fluorouracil induced an increase in micronucleus frequency, which could significantly be enhanced by the concurrent application of 2,6-dihydroxypyridine, an inhibitor of dihydropyrimidine dehydrogenase. The 5-fluorouracil concentration necessary to reach maximal genotoxic effects could be reduced to half in the presence of inhibitor 2,6-Dihydroxypyridine alone and the naturally occurring enzyme substrate uracil did not induce micronucleus formation. Combined application of the chemotherapeutic agent 5-fluorouracil and an inhibitor of its could reduce side-effects by lowering the effective dose of the active drug. With this study we provide further support for the usefulness of this concept.

Characterization of cadherin-4 and cadherin-5 reveals new aspects of cadherins

Several properties of cadherin-4 and cadherin-5 were characterized by using the cDNA transfection approach. The proteins of both cadherins had a relative molecular mass of about 130 kDa and were present at the cell periphery, especially at cell-cell contact sites. These cadherins were easily digested with trypsin, and Ca2+ protected cadherin-4, but not cadherin-5, from the digestion. In immunoprecipitation, cadherin-4 co-precipitated with two major proteins of 105 kDa and 95 kDa, respectively. The 105 kDa and the 95 kDa proteins are likely to correspond to alpha- and beta-catenins. Cadherin-5 co-precipitated with only one major protein of 95 kDa, but seems to associate with the 105 kDa protein. On the other hand, plakoglobin or gamma-catenin did not co-precipitate well with either cadherin-4 or cadherin-5 in immunoprecipitation, but plakoglobin also appears to associated weakly with these cadherins. Cadherin-4 transfectants aggregated within 30 minutes in a cell aggregation assay, but cadherin-5 transfectants did not aggregate under the same conditions. Furthermore, the transfectants of chimeric cadherin-4 with cadherin-5 cytoplasmic domain showed cell aggregation activity comparable to that of wild-type cadherin-4 transfectants, whereas the transfectants of chimeric cadherin-5 with cadherin-4 cytoplasmic domain did not show appreciable cell aggregation, suggesting that the extracellular domains of cadherins, in conjunction with their cytoplasmic domains, play an important role in cell aggregation activity. These results show that cadherin-4 is very similar to the classical cadherins, whereas cadherin-5 is functionally as well as structurally distinct from classical cadherins.

Localization of dynamin: widespread distribution in mature neurons and association with membranous organelles

Tissue distribution and intracellular localization of dynamin by immunoblotting and immunocytochemistry is investigated in this study. Dynamin was widely expressed in all the neurons we examined, and was especially abundant in the central nervous system after maturation, although its expression presented regional heterogeneity. Dynamin was present most abundantly in cerebellar Purkinje cells and hippocampal pyramidal cells, and to a lesser extent in motor neurons and peripheral nerves. However, dynamin was nearly absent in cells such as anterior pituitary cells and adrenal medullary cells which secrete mainly dense cored vesicles. Dynamin was localized not only in cell bodies, axons, and synapses but also in dendrites. Subcellular fractionation indicated that dynamin existed in the membrane fraction as well as in the soluble fraction. In ligated peripheral nerves, dynamin colocalized with tubulovesicular membranous organelles transported mainly anterogradely. By transfection of dynamin cDNA into mouse fibroblast L-cells, we showed it colocalized with some membranous organelles but not with microtubules. Our results show that dynamin is associated with membranous organelles in vivo, although a certain amount of dynamin also exists in the soluble fraction and is distributed diffusely throughout mature neurons. The data suggest that dynamin's fundamental role involves membrane trafficking in neurons in the central nervous system rather than in sliding microtubules as a motor protein.

The 220-kD protein colocalizing with cadherins in non-epithelial cells is identical to ZO-1, a tight junction-associated protein in epithelial cells: cDNA cloning and immunoelectron microscopy

We previously identified a 220-kD constitutive protein of the plasma membrane undercoat which colocalizes at the immunofluorescence microscopic level with cadherins and occurs not only in epithelial M., S. Yonemura, A. Nagafuchi, Sa. Tsukita, and Sh. Tsukita. 1991. J. Cell Biol. 115:1449-1462). To clarify the nature and possible functions of this protein, we cloned its full-length cDNA and sequenced it. Unexpectedly, we found mouse 220-kD protein to be highly homologous to rat protein ZO-1, only a part of which had been already sequenced. This relationship was confirmed by immunoblotting with anti-ZO-1 antibody. As protein ZO-1 was originally identified as a component exclusively underlying tight junctions in epithelial cells, where cadherins are not believed to be localized, we analyzed the distribution of cadherins and the 220-kD protein by ultrathin cryosection immunoelectron microscopy. We found that in non-epithelial cells lacking tight junctions cadherins and the 220-kD protein colocalize, whereas in epithelial cells (e.g., intestinal epithelial cells) bearing well-developed tight junctions cadherins and the 220-kD protein are clearly segregated into adherens and tight junctions, respectively. Interestingly, in epithelial cells such as hepatocytes, which tight junctions are not so well developed, the 220-kD protein is detected not only in the tight junction zone but also at adherens junctions. Furthermore, we show in mouse L cells transfected with cDNAs encoding N-, P-, E-cadherins that cadherins interact directly or indirectly with the 220-kD protein. Possible functions of the 220-kD protein (ZO-1) are discussed with special reference to the molecular mechanism for adherens and tight junction formation.

Centrosome repositioning immediately following karyokinesis and prior to cytokinesis

The behaviour of the centrosome immediately following cell division in tissue culture cells has been investigated. We find that following karyokinesis, but preceding cytokinesis, sister centrosomes relocate from the spindle poles to a position adjacent to the intercellular bridge. This repositioning is accompanied by the appearance of a microtubule bundle that extends from the poleward region of the cell to the centrosome and increases in length as the centrosome approaches the intercellular bridge. Disruption of this bundle with colcemid interrupts centrosome repositioning. In contrast, centrosome repositioning persists in late mitotic cells grown in the presence of cytochalasin D. However, the position of the microtubule-centrosome complex within the cell is randomized suggesting that the path, but not the process, of centrosome repositioning is dependent on an intact actin filament network. This study points out, for the first time, that the complex migration of the centrosome preceding mitosis is paralleled by an equally complex set of events following cell division. We suggest that post-mitotic centrosome repositioning may play a role in ensuring that daughter cells have equal but opposite polarity and may reflect an interrelationship between the establishment of the interphase cytoskeleton and the completion of cytokinesis.

Pathways of internalization of the hCG/LH receptor: immunoelectron microscopic studies in Leydig cells and transfected L-cells

Monoclonal anti-receptor antibodies were used to study the cellular traffic of the hCG/LH receptor by immunoelectron microscopy. The LHR38 antibody was shown to bind to the extracellular domain of the receptor but not to interfere with hormone binding, adenylate cyclase activation or with the rate of internalization of the receptor. Pig Leydig cells and a permanent L-cell line expressing the LH receptor were used for the study. Incubation with LHR38-gold complexes showed the LH receptors to be randomly distributed over the cell surface including the clathrin coated pits. The LH receptors were internalized via a route including coated pits, coated vesicles and multivesicular bodies to lysosomes. This route is different from that observed for beta-adrenergic, muscarinic, and yeast mating factor receptors and considered previously as possibly general for G-protein-coupled receptors. The use of [125I]LHR38 allowed precise measurement of the rate of internalization, showing the existence of a constitutive pathway which was increased 11-fold by hormone administration. Double labeling experiments suggested that the hormone (hCG-Au15nm) and the receptor (labeled with LHR38-Au5nm) have similar routes of endocytosis, both of them being degraded in lysosomes. Studies of the reappearance of LHR38-Au5nm on the surface of the cells and the use of monensin indicated that only a very small proportion of the receptor molecules were recycled to the cell surface. The distribution and the intracellular pathways of LH receptors are very similar in Leydig cells and transfected L-cells. This opens the possibility of using the latter to study, by in vitro mutagenesis, the molecular mechanisms involved in the cellular traffic of LH receptors.

Intracellular localization of the HLA class II gene products in transfected mouse L cells

To investigate the impaired cell surface expression of human major histocompatibility antigen (HLA) in transfected L cells, we examined their intracellular localization by immunocytochemistry. HLA class II molecules produced in transfected L cells were mainly detected in the intracellular vesicles and in the nuclear envelope as granular precipitates. The results suggest that the intracellular transport of the newly synthesized molecules in transfected L cells is impaired at some point along the pathway from the rough endoplasmic reticulum (RER) to the medial-, trans-Golgi apparatus.

The polypeptide encoded by the cDNA for human cell surface antigen Fas can mediate apoptosis

Mouse anti-Fas monoclonal antibody has a cytolytic activity on human cells that express the antigen. Complementary DNAs encoding the cell surface antigen Fas were isolated from a cDNA library of human T cell lymphoma KT-3 cells. The nucleotide sequence of the cDNAs revealed that the molecule coding for the Fas antigen determinant is a 319 amino acid polypeptide (Mr 36,000) with a single transmembrane domain. The extracellular domain is rich in cysteine residue, and shows a similarity to that of human tumor necrosis factor receptors, human nerve growth factor receptor, and human B cell antigen CD40. Murine WR19L cells or L929 cells transformed with the human Fas antigen cDNA were killed by the anti-Fas antibody in the process known as apoptosis.

Anchoring and degradation of glycolipid-anchored membrane proteins by L929 versus by LM-TK- mouse fibroblasts: implications for anchor biosynthesis

Although many cells anchor surface proteins via moieties that are sensitive to phosphatidylinositol-specific phospholipase C (PI-PLC), the anchor moieties of surface proteins of mouse L929 cells resist PI-PLC. By constructing stable hybrids between L929 and lymphoma cells that express glycolipid-anchored proteins in a PI-PLC-sensitive form, we show that PI-PLC resistance behaves as a recessive trait. Since putative mannolipid precursors of the lipid anchors bear alkali-labile substituents which make them resist PI-PLC, these observations are most simply interpreted by postulating that L929 lacks a critical anchor deacylase. Unlike the L929 cell line, two of its descendants, the LM cell line and its thymidine kinase-negative variant (LM-TK-), do not express glycolipid-anchored proteins on their surface. Moreover, unlike L929 cells, LM-TK- cells rapidly inactivate at least one lipid-anchored enzyme in a compartment sensitive to acidotropic amines and leupeptin. By fusion of LM-TK- cells to mouse Thy-1- lymphoma mutants and monitoring of surface expression of lipid-anchored proteins, we assign LM-TK- to lymphoma mutant complementation group H. This genetic assignment is matched by analysis of mannolipids of L929, LM-TK-, wild-type, and class H lymphoma mutant cells: striking similarities are seen between the two wild-type cells by contrast to the mutants. Since the differences pertain to lipids which have properties consistent with their being anchor precursors, we suggest that LM-TK- has a lesion in the synthesis of anchor precursor mannolipids.

A rapid method for screening vaccinia virus recombinants

A rapid and small-scale method for screening vaccinia virus recombinants employing micrococcal nuclease is described. This protocol utilizes the differential sensitivity of cellular and viral DNA to the nuclease, which can be selectively activated by addition of Ca2+ and inactivated by elimination of Ca2+. Two to five micrograms of viral DNA can be obtained from one infected L cell plate (50 mm) after overnight incubation.

Detection of individual fluorescently labeled reovirions in living cells

Reovirus serotype 1 (Lang) can be conjugated with rhodamine B or fluorescein isothiocyanate in a way that preserves viral infectivity. We have used epifluorescence microscopy to detect individual virions bound to the surface of cells and to follow in real time the early stages of reovirus infection in living cells. Following uptake of the virus into endocytic vesicles, the movement of these vesicles can be observed readily. The vesicle movement is inhibited by nocodazole or colchicine, consistent with previous findings that the movement of intracellular vesicles is often microtubule-based.

Ultrastructural changes during lysis of L929 target cells by class II-restricted influenza virus-specific murine cytotoxic T-lymphocyte clones

Lysis of virus-infected L929 target cells transfected with the H-2 class II IAk gene by class II-restricted influenza virus-specific murine cytotoxic T lymphocyte (CTL) clones was studied by electron microscopy and compared with lysis of L929 cells by class I-restricted CTL clones. T lymphocytes predominantly approached the basal surface of target cells grown on a plastic dish and also approached uninfected L929 target cells, although virus maturation exhibited no polarity with respect to the cell surface site. After incubation for 30 min, the target cell nuclei began to change: chromatin became irregularly redistributed and aggregated, and the nuclei appeared swollen. Later, electron-dense and -light areas of nuclei became segregated, and the cytoplasm became disorganized with many vacuoles. The ultrastructural changes of target cells during lysis by class I- and class II-restricted CTL clones appeared to be similar. These findings and other cytotoxicity data of class I and class II CTLs are discussed.

Endocytosis of liposomes containing lysosomal proteins increases intracellular protein degradation in growing L-132 cells

We have used a new approach to test the possible participation of lysosomes in the degradation of long-lived proteins. Rat liver lysosomal proteins were introduced, via multilamellar liposomes, into L-132 cells. Viability and protein synthesis were not impaired by this treatment. The liposomal content was released into the lysosomes of the cultured cells, as revealed by ferritin uptake and electron microscopy. Degradation rates of long-lived proteins increased with the uptake of lysosomal proteases. However, the increased protein degradation of chloroquine and leupeptin, in contrast to the inhibition by these reagents of the increased protein degradation of cells 'starved' of serum (step-down conditions). This approach opens a new way of investigating the degradation of intracellular proteins in cultured cells.

Expression of multiple tau isoforms and microtubule bundle formation in fibroblasts transfected with a single tau cDNA

Tau proteins are a class of low molecular mass microtubule-associated proteins that are specifically expressed in the nervous system. A cDNA clone of adult rat tau was isolated and sequenced. To analyze functions of tau proteins in vivo, we carried out transfection experiments. A fibroblast cell line, which was transfected with the cDNA, expressed three bands of tau, while six bands were expressed in rat brain. After dephosphorylation, one of the three bands disappeared, demonstrating directly that phosphorylation was involved in the multiplicity of tau. Morphologically, we observed a thick bundle formation of microtubules in the transiently and stably tau-gene-transfected cells. In addition, we found that the production of tubulin was prominently enhanced in the stably transfected cells. Thus, we suppose that tau proteins promote polymerization of tubulin, form bundles of microtubules in vivo, and play important roles in growing and maintaining nerve cell processes.

Mutations in the cytoplasmic domain of the 275 kd mannose 6-phosphate receptor differentially alter lysosomal enzyme sorting and endocytosis

The cation-independent mannose 6-phosphate receptor (Cl-MPR) sorts newly synthesized lysosomal enzymes in the Golgi and endocytoses extracellular lysosomal enzymes. To determine the role of the 163 amino acid cytoplasmic domain of the Cl-MPR in these functions, receptor-deficient mouse L cells were transfected with normal bovine Cl-MPR cDNA or cDNAs mutated in the cytoplasmic domain. The normal Cl-MPR functioned in sorting and endocytosis. Mutant receptors with 40 and 89 residues deleted from the carboxyl terminus of the cytoplasmic tail functioned normally in endocytosis, but were partially impaired in sorting. Mutant receptors with larger deletions leaving only 7 and 20 residues of the cytoplasmic tail were defective in endocytosis and sorting. A mutant receptor containing alanine instead of tyrosine residues at positions 24 and 26 was defective in endocytosis, and partially impaired in sorting. Receptors deficient in endocytosis accumulated at the cell surface. These results indicate that the cytoplasmic domain of the Cl-MPR contains different signals for rapid endocytosis and efficient lysosomal enzyme sorting.

Glycolysis in permeabilized L-929 cells

Mouse L-929 cells permeabilized with dextran sulphate (DSP cells) carry out glycolysis when supplemented with glucose, ATP and NAD+ in a suitable incubation buffer. Glycolytic rates were linear and generally independent of cell density over the range examined (1 x 10(6)-10 x 10(6) cells/ml). Electron microscopy revealed characteristic changes in DSP cell ultrastructure, notably for nuclei and mitochondria. Some cells lacked plasma membranes, while others appeared intact. In the latter case, estimates of the lesion size in plasma membranes were obtained from volume of distribution studies using 14C-labelled proteins, and infiltration of fluorescein isothiocyanate dextran. The results indicated the presence of lesions large enough to allow globular proteins of about 400 kDa to cross the cell surface. In spite of that, only about 10% of total cell protein exited from DSP cells during a 30 min incubation period. We propose that none of the glycolytic enzymes in DSP cells can exist completely in solution in the 'cytosol', suggesting extensive enzyme organization. The results are interpreted within the broader picture of metabolic organization in animal cells and the nature of the 'cytosol'.

Contrasting views on the organization of cytoplasm

The widely held conception of cytoplasm as a concentrated solution of dissolved proteins and other macromolecules, metabolites and inorganic ions, within which the various organelles and other formed elements are suspended appears to be a gross over-simplification. Evidence to be reviewed briefly here, from a wide variety of experiments and cell types, indicates that a much more extensive organization exists, in animal cell cytoplasm at least. Results from experiments on dextran sulfate permeabilized L-929 cells will be presented which support that organized paradigm. It seems likely that this intracellular architecture also exerts a strong influence on the water in the regions adjacent to it, resulting in the generation of altered aqueous phase physical properties compared to those of ordinary aqueous solutions. This analysis suggests consequences of far reaching importance to our understanding of cell structure and function.

[Enucleation and reconstruction of murine L-cell fibroblasts]

Two types of teflon chambers are suggested for the procedures of enucleation and reconstruction of cells cultivated in the monolayer. The first chamber simplifies the enucleation and permits performing it on the standard cover glasses with a small volume of medium with cytochalasin B. The second chamber permits purifying the karyoplast fraction from intact cells by their adhesion on the cover glasses. Then the karyoplasts are sedimented by centrifugation on cytoplasts located on the cover glasses. This procedure promotes sticking of fragments and their subsequent fusion in the presence of polyethylene glycol. In total the number of reconstructed cells increases many times.

Spontaneous expulsion of micronuclei by enucleation in the micronucleus assay

The effect of enucleation on the frequency of micronuclei induced by mitomycin C (MMC) and vincristine (VCR) was examined in mouse L-929 cells enucleated with cytochalasin B (Cyt-B). Approximately 30% of the L-929 cells became enucleated cells during the 8-h incubation in medium containing 8 micrograms/ml of Cyt-B. Using this enucleation technique, we estimated the reduction rate of 2 mutagen-induced micronuclei by enucleation. Treatment with MMC caused a dose-dependent induction of micronuclei in L-929 cells, with the reduction rate being 38.6% at the lowest dosage (0.0125 microgram/ml), which induced mostly mono-micronuclei in L-929 cells, and 6.8% at the highest dosage (0.1 microgram/ml), which induced many multi-micronuclei. Furthermore, VCR also induced micronuclei in a dose-dependent way in L-929 cells, and the same tendency for micronucleus reduction as with MMC was observed. The reduction rate of micronucleated cells by enucleation was estimated to be about 31-39% when the micronucleated cells contain mono-micronuclei. Therefore, the rate of reduction is affected by the number of micronuclei per cell, and the reduction depends on the increase in the number of micronuclei per cell.

[Karyotype analysis of clone L929 murine fibroblasts by using differential chromosome staining]

Karyological analysis of mouse fibroblasts L929 has been carried out using the differential staining of chromosomes (44-58% of the total chromosome number), and their derivatives, i.e. markers of the particular clone. Normal, non-rearranged chromosomes are mainly present in 1-3 copies, while the markers are available as a single copy only. The frequency of occurrence of diverse chromosomes differs from cell to cell, the total number of chromosomes in the cells being not constant. The modal class consists of 62-64 chromosomes. Two new chromosome markers were found after a repeated karyological analysis one year after the cultivation of cells under the standard conditions. A possible role of some chromosome aberrations in the process of transformation of mouse fibroblasts is discussed. The particular attention is given to alteration of chromosome 15.

[Reorganization of the tubulin and vimentin components of the cytoskeleton as affected by the action of hypotonia on L cells]

Mouse transformed fibroblasts of line L show a disruption of the microtubule system and an appearance of intermediate organizing centres after 0.5-1 min of incubation in the hypotonic medium. After 30-60 min of hypotonic treatment the recovery of microtubules and the thickening of intermediate filaments around the nucleus are observed, which promotes a disguise of intermediate organizing centres.

Application of a small microcomputer to cell image analysis

Solutions to three problems in using small microcomputers for interactive cell image analysis are discussed. (1) To allow interactive processing of up to 62 X 88 pixels on inexpensive screens, data can be displayed in gray levels with an approximate logarithmic grading. Each pixel is composed of 32 screen coordinates, applying the dither matrix method to avoid artificial structures. (2) To mark special regions of interest in the image, a graphic cursor, handled from the keyboard, was implemented. (3) To evaluate parts of the image, as outlined by the cursor, the program must distinguish whether a particular pixel is outside, inside or on the border of the region. The developed algorithms permit practical interactive evaluation of cell images on a small microcomputer, with no image analysis implementation. However, it is necessary that the assembly language of the microprocessor be available for some sophisticated programming and that the operating system support graphic facilities with an appropriate resolution.

[Centrioles in the cell cycle of L cells]

The structure of centrosome in non-synchronous L-cells culture during the cell cycle has been studied. In mitosis, mother and daughter centrioles, which differ in their ultrastructure, are located perpendicularly in the pole of the spindle. Microtubules, meeting in the pole area terminate mainly in electron-dense clottings of fibrillar matter surrounding the diplosoma. In telophase, disjunction of mother and daughter centrioles begins. At the beginning of G1-period, centrioles move off from each other for several micron, and then draw together again without forming diplosome. Pericentriolar satellites form on mother centriole of some cells at this time, they disappear at the beginning of S-period, replication of centrioles begins; daughter centrioles reach the size of mother centrioles in anaphase. During growth and maturation, centrioles in L-cells undergo structural changes similar to those described for SPEV cells (Vorob'ev, Chentsov, 1982). Several types of meeting points for microtubules exist in L-cells during the whole interphase: surface of centrioles per se, pericentriolar satellites, free foci.

Resistance to the cytolytic action of lymphotoxin and tumor necrosis factor coincides with the presence of gap junctions uniting target cells

The resistance of target cells to the cytolytic action of lymphotoxin (LT) and recombinant tumor necrosis factor (rTNF) has been investigated by using clonally derived cell lines with defined gap junction-mediated, intercellular communication properties. Gap junction-competent Chinese hamster ovary cells are normally insensitive to the action of LT/TNF. However, treatment with 12-o-tetradecanoylphorbol-13-acetate, which promotes the loss of gap junctions, or culturing at low cell density to reduce intercellular contacts, significantly increased their sensitivity to LT/TNF. The LT/TNF-sensitive murine CL-1D and L929 cell lines, which in normal culture conditions are unable to form gap junctions, were not changed in their susceptibility to LT/TNF after treatment with phorbol ester or low culture density. However, the formation of gap junctions by CL-1D can be promoted by treatment with 8-bromo-cyclic adenosine monophosphate (1 mM), and this treatment completely suppressed the ability of LT and rTNF to kill CL-1D. Additionally, the LA25-normal rat kidney cell line, which is infected with a temperature-sensitive mutant of Rous sarcoma virus (LA25), is gap junction-competent and resistant to the effects of LT at the restrictive temperature (39 degrees C). However, when shifted to the permissive temperature (33 degrees C), LA25-normal rat kidney cells express the pp60v-src viral gene product, lose their ability to form gap junctions, and become sensitive to the lytic activity of LT. The results demonstrate that the expression of the retroviral pp60v-src, a tyrosine protein kinase, is sufficient to render cells susceptible to the lytic effects of LT and rTNF. Collectively, these experiments demonstrate a strong correlation between the resistance of target cells to the action of LT/TNF and their ability to cooperate metabolically through gap junctions. The results do not completely exclude the possibility that other mechanisms, such as LT receptor modulation, are also occurring under these experimental conditions. These data also suggest that a possible physiologic function of the stable cytotoxic lymphokines is to induce cytolysis/cytostasis of cells that have lost gap junctional contact, such as those in the process of mitosis or metastasis that have separated from the main tissue mass.

The higher order structure of the centromere

The architecture of the centromere region of mouse chromosomes has been studied in cells grown in the presence of 5-azacytidine. This drug interferes with normal condensation producing elongated centromere regions. It has been found that this effect is reversible in the presence of the drug, allowing the observation of the repackaging of the extended centromere into a structure exhibiting native centromere morphology. Light microscopy as well as transmission and scanning electron microscopy of this condensation process suggests that the native centromere is formed by the helical folding of a subfiber with an approximate diameter of 100 nm. This fiber is in turn composed of loops of the 30-nm fiber class. The boundary between successive gyres of the subfiber are obscured at the completion of condensation resulting in the formation of a homogenous 250- to 300-nm fiber that is the native centromere. These observations provide evidence for an additional level of chromatin organization within the metaphase chromosome.

Association of reovirus proteins with the structural matrix of infected cells

The interaction of reovirus with the cytoskeleton was investigated. The soluble components of infected cells were extracted with the nonionic detergent NP-40 in a physiological buffer, and a cytoskeletal extract was prepared from the detergent-insoluble fraction. We observed a selective association of viral-specified products with the cytoskeleton that was temporally controlled. Viral dsRNA appeared first on the framework but after several hours was found also in the soluble phase, encapsidated in mature virions. The initial viral translation products were associated exclusively with the soluble fraction, but concomitant with the appearance of dsRNA, viral proteins microNS and sigma 3 were detected on the cytoskeleton. Several hours later, all viral proteins were detected on the framework. Viral polypeptide microNS exhibited unique spatial distribution patterns that correlated with viral assembly: Before dsRNA replication, it appeared as diffusely distributed protein; a few hours later, it was detected in punctate foci interconnected by tiny filaments; several hours later, it appeared as an extensive fiber network that traversed the foci. The other viral proteins were detected only within viral foci. MicroNS remained bound to the matrix fraction after treatment with DNase, Mg2+, and high salt, treatments that released other viral proteins. This distribution pattern was virus-directed because passage of virus at high multiplicity of infection induced mutations that prevented assembly of the microNS-coated filament organization. A small fraction of the viral-specified products that included polypeptide microNS, but not viral dsRNA, was coprecipitated from cytoskeletal extracts with proteins of mol wt approximately 55K by monoclonal antibodies that recognized tubulin and vimentin. Disruption of this interaction by long exposure to colchicine did not prevent association of viral proteins or RNA with the matrix, indicating that viral products were not transported through these interactions. The results indicate that reovirus morphogenesis includes temporal and spatial controls not described previously.

The synthesis of a particle-forming cellular protein is enhanced by Mengo virus infection

We have detected a cellular protein which not only escapes the shutoff of host translation induced by Mengo virus, but is synthesized in increasing amounts during Mengo virus infection. The protein has an apparent molecular weight of 20,000 and is contained in a remarkably stable cytoplasmic particle with a sedimentation coefficient of approximately 16 S in sucrose gradients. In the electron microscope this particle appears as a sphere of approximately 12 nm diameter. The synthesis of the protein is stimulated in mouse L cells and in HeLa cells infected with Mengo virus. Its synthesis cannot be induced, however, by stress (heat) or by infection with reovirus.

[Ultrastructure of the centrosome in L cells]

Three types of microtubule-organizing centers are present in the interphase L-cells: centriolar matrix, pericentriolar satellites, and electron-dense bodies that are not attached to the centrioles. Different types of microtubule-organizing centers may be present simultaneously in the same centrosome. In most of the cells some microtubules have their proximal ends free, rather than attached to the microtubule-organizing center. A network of intermediate filaments is condensed around the centrosome. The intermediate filaments run from the centrosome parallel to the microtubules. Although the filaments are often in close proximity to the centrioles and microtubules, direct contacts between them are rare. The intermediate filaments have convergence foci of their own in the centrosome.

[Fatty conversion of mouse fibroblasts of the L-929 line induced by cysticerci of the cat tapeworm]

Effect of exometabolites of cysticerci of H. taeniaeformis on morphological features of transformed fibroblasts was investigated using L-929 cells. Studies on histochemistry and ultrastructure of L-929 cells treated with the cysticercal exometabolites induced a fatty conversion of these cells. It is proposed that the exometabolites in question may exert their influence on differentiation degree in the in vitro long-term cultivated fibroblasts-like cells.

The effect of glutathione depletion by diamide, diethyl maleate or buthione sulfoximine on the surface structure of mouse L-cells

Radiosensitizers that act by reducing glutathione levels have been studied by many workers as agents to enhance the killing of hypoxic tumour cells. In this paper we describe a scanning electron microscope (SEM) study of the surface morphology of mouse L-cells after exposure to three of these: diazenedicarboxylic acid bis N,N-dimethylamide (diamide), DL-buthionine-S,R-sulfoximine (BSO) and diethyl maleate (DEM). Diamide at 0.1 to 0.6 mMol/L for 10 min produced large blebs on the cell surface as seen in the SEM. Transmission electron microscope (TEM) images show that these are clear, featureless regions of cytoplasm. BSO treatment for 24 h at 0.5 to 2.0 mMol/L, by contrast, left the surface similar to control cells. DEM at 0.5 mMol/L for 2 h produces small blebs over the cell surface and a reduction in the number of microvilli. A combined 24 h BSO treatment with 2 h of DEM produced large blebs, which were similar in TEM micrographs to those produced by diamide. Thus, although all three sensitizers reduce glutathione levels, they have different effects on cellular morphology and hence such secondary effects may account for the different degrees of radiation sensitization seen with these agents.

[Tolerance of different cell types for hypotonic action]

The behavior of cells with different structure of cytoskeleton was studied in the hypotonic media: protoplasts, embryonal mouse fibroblasts and transformed mouse fibroblasts (L-line). Protoplasts were most sensitive to the hypotonic media. They began to disrupt in the hypotonic medium 4:1, and in the hypotonic medium 1:7 a complete lysis of cells was observed. Transformed mouse fibroblasts were disrupted in the medium diluted 1:15, while embryonal mouse fibroblasts were not disrupted in the medium diluted 1:31. Moreover, in the hypotonic conditions an essential difference was observed between the cells studied. Embryonal mouse fibroblasts are more tolerant to the hypotonic conditions than L-cells and protoplasts. It is suggested that the cytoskeleton may define the cell tolerance in hypotonic media.

Sequence of centromere separation: a mechanism for orderly separation of dicentrics

Stable dicentric chromosomes from three mouse cell lines (viz., SEWA Rec4, brain tumor, and L-cells), as well as a human t(9;11) line were analyzed for the sequence in which the two centromeres separate. At prometaphase, as well as in many cells at midmetaphase, the dicentrics express the two centromeres in the form of two primary constrictions. As the cell advances to late metaphase, one of the constrictions loosens the two chromatids so that eventually there is no connection between them. The other centromere stays intact during this period and separates into two units at the metaanaphase junction along with the rest of the genome. The centromere that separates prematurely (out-of-phase) usually is the same in a given dicentric. It is proposed that such a prematurely separating centromere does not function as active element during chromatid migration. Apparently, in dicentrics some sort of control is exerted to eliminate the functioning of one centromere. The nature of such control is not understood at this time. The mouse dicentrics "synthesize" only one kinetochore as definable by antikinetochore antibody studies.

[Dependence of the redistribution of ligand-receptor complexes in cultured cells on the type of growth and on the cell cycle phase]

The process of active redistribution of ligand-receptor complexes on the surface of both suspension (LS) and adapted for growing in monolayer (LMS) sublines of mouse fibroblasts L was studied. The binding of ligands to its specific receptors on the surface of the LS cells induced an accumulation of ligand-receptor complexes on one pole of a cell with the formation of a typical cap. Under the same conditions in the LSM cells the cleaning of processes and lamello-plasma surfaces from the ligand-receptor complexes was registered. The binding of ligands to the surface of the LSM cells, detached with EDTA, induced the same capping process, as in the case of the LS cells. No differences were found in the redistribution capacity of the ligand-receptor complexes in synchronized cultures of the LS and LSM cells in the G1 and S phase of the cycle. But such a redistribution was not registered on the surface of cells in metaphase and anaphase. The accumulation of ligand-receptor complexes was found in the region of cleavage between daughter cells in telophase. These results are in a good agreement with the well-known data on the changes in the cytoskeleton organization during transition from a monolayer to a suspension state and during mitosis.

Organization within the mammalian kinetochore

The organization within the mammalian kinetochore was examined using whole-mount electron microscopic techniques on chromosomes digested with restriction enzymes or micrococcal nuclease. These preparations revealed that a portion of the kinetochore is highly resistant to nuclease digestion and can be visualized as a discrete structure. The relationship of this structure to the remainder of the chromosome suggests that it represents the outer kinetochore plate. The plate is composed of a series of fibrillar loops that are arranged in a parallel array along the plane of the plate. These fibers are 25-30 nm in diameter. The morphology, particulate substructure, and ultimate susceptibility to nuclease digestion suggest that these fibers contain DNA. A model is presented that suggests that the outer plate contains the apexes of chromatin loops that originate within the body of the primary constriction.

Internalization and transport of mouse beta-interferon into the cell nucleus

An electron microscopic technique employing postembedding immunolabeling was used to identify unmodified, intracellular MuIFN-beta molecules. The MuIFN-beta was rapidly internalized by receptor-dependent endocytosis and within three minutes a majority of internalized MuIFN-beta molecules was detected within the cell nucleus.

Endonuclease banding of isolated mammalian metaphase chromosomes

Evidence is presented that endonuclease digestion of isolated, unfixed chromosomes results in the production of banding patterns similar to those produced by digestion of fixed, air-dried chromosomes. Mouse L cell chromosomes were isolated under acidic or relatively neutral pH conditions, exposed in situ (as wet mounts on glass slides) or in vitro (in suspension) to micrococcal nuclease, Alu I or Eco RI, treated with a buffered salt solution, and stained with Giemsa. After any of these endonuclease treatments in situ, the centromeric regions of the chromosomes were intensely stained, characteristic of the C-banding observed in fixed chromosomes exposed to the same treatments. Although the fixed chromosomes were morphologically well-preserved after endonuclease digestion, the morphology of chromosomes digested in situ was variable, ranging from normal to swollen to highly distorted chromosomes. In the latter, the endonucleases induced dispersion of non-C-band chromatin; however, C-bands were still apparent as condensed, differentially-stained regions. Exposure of isolated chromosomes to Alu I in vitro also resulted in well-defined C-banding and led to the extraction of about 70% of the chromosomal DNA. From these results, the mechanism of endonuclease-induced C-banding appears to involve the dispersion and extraction of digested chromatin.

[Ultrastructural aspects of the process of Salmonella typhi bacterial interaction with L929-line cells]

The study of the use of scanning electron microscopy and the analysis of the initial stages of interaction between S. typhi and eukaryotic cells by the method of three-dimensional reconstruction has revealed that the infective agent penetrates into the cytoplasm on the principle of internalization. The internalization of S. typhi occurs with the active participation of the eukaryotic cells which, at the beginning, envelopes the bacteria with its processes, and the infective agents firmly adhere to the glycocalyx of the host cell by means of special fimbria-like formations differing from fimbriae by their lesser rigidity and thickness; then the microbes fixed to the membrane penetrate inside the cell without destroying its cytoplasmic membrane. Differences in the processes of the interaction of eukaryotic cells with S. typhi initial strain 238 and its variant free from the plasmid with a molecular weight of 6 Md, characterized by its lower capacity for association with cells of continuous cell culture L929, have been revealed. The factors stimulating the ingestion of S. typhi by eukaryotic cells are under study at present.

Localization of DNAase I-sensitive sequences to specific regions of interphase nuclei

Active or potentially active gene loci are preferentially sensitive to DNAase I digestion. Cedar and colleagues used this DNAase I sensitivity to label active sequences preferentially by nick translation of nuclei and chromosomes. Using biotinylated nucleotides and immunofluorescence detection, we have looked for compartmentalization of DNAase I-sensitive sequences by nick translation of nuclei maintained as three-dimensional structures. Labeled sequences in mouse L cells are preferentially localized at the nuclear periphery in both permeabilized nuclei and frozen sections. In newt and chicken nucleated erythrocytes, labeled regions are at borders of condensed chromatin masses along interchromatin channels communicating with the nuclear periphery. Control experiments indicate that nick translation of nuclei preferentially labels highly expressed genes and that the preferential localization of DNAase-I sensitive regions is probably not a consequence of fixation artifacts or selective nuclear permeability to the labeling reagents.

Centromere organization in chromosomes of the mouse

The ultrastructure of the centromere region of chromosomes from mouse L929 cells treated with agents that affect centromere condensation have been examined using light, transmission electron, and scanning electron microscopic techniques. Micrographs of expanded centromeres from treated chromosomes illustrate that both the biarmed chromosomes that were generated by Robertsonian fusion during the past history of the strain and the functional centromere of the multicentromeric marker chromosomes display a prominent gap. This gap probably represents the original site of association of the acrocentric chromosomes and is also the site of the kinetochore. Despite the multicentromeric nature of the marker chromosome a single pair of kinetochores were found only at the central heterochromatic region. The functional implications of these structural findings are discussed.

[Morphological characteristics of the brain lesions in mice infected with a homogenate of L cells latently infected with the scrapie agent]

Degeneration of neurons of the Ammon horn lower branch both in the early and terminal stages of the disease of mice infected with the homogenate of L cells latently infected with the scrapie agent (the L-S system) was frequently detected alongside with brain lesions typical of slow infections (vacuolation). Examinations of chromosomes in metaphase plates of L-S cells carried out by several methods including the TAC system for texture analysis of the image (Leutz, BRD) revealed three marker chromosomes new for continuous L cells, the appearance of true chromatid translocations as well as significant changes in chromosome numbers. Besides, ultrastructural features of L-S cells at later stages of cultivation were revealed. It is assumed that the active effect of the scrapie agent on L cells infected with it resulted in the emergency of a new antigen capable to induce selective affection of the neurons of the Ammon horn lower branch in susceptible mice.