Compensation mechanism in tumor cell migration: mesenchymal-amoeboid transition after blocking of pericellular proteolysis.
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Invasive tumor dissemination in vitro and in vivo involves the proteolytic degradation of ECM barriers. This process, however, is only incompletely attenuated by protease inhibitor-based treatment, suggesting the existence of migratory compensation strategies. In three-dimensional collagen matrices, spindle-shaped proteolytically potent HT-1080 fibrosarcoma and MDA-MB-231 carcinoma cells exhibited a constitutive mesenchymal-type movement including the coclustering of beta 1 integrins and MT1-matrix metalloproteinase (MMP) at fiber bindings sites and the generation of tube-like proteolytic degradation tracks. Near-total inhibition of MMPs, serine proteases, cathepsins, and other proteases, however, induced a conversion toward spherical morphology at near undiminished migration rates. Sustained protease-independent migration resulted from a flexible amoeba-like shape change, i.e., propulsive squeezing through preexisting matrix gaps and formation of constriction rings in the absence of matrix degradation, concomitant loss of clustered beta 1 integrins and MT1-MMP from fiber binding sites, and a diffuse cortical distribution of the actin cytoskeleton. Acquisition of protease-independent amoeboid dissemination was confirmed for HT-1080 cells injected into the mouse dermis monitored by intravital multiphoton microscopy. In conclusion, the transition from proteolytic mesenchymal toward nonproteolytic amoeboid movement highlights a supramolecular plasticity mechanism in cell migration and further represents a putative escape mechanism in tumor cell dissemination after abrogation of pericellular proteolysis. (+info)
Studies on changes in the nuclear helices of Amoeba proteus during the cell cycle.
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The fine structure of the nuclei of synchronously growing cell population of Amoeba proteus was studied at I-h intervals during the interphase. This study showed that the nuclear helices undergo increases in their number at certain stages during interphase. These changes were found to correlate with ultrastructural changes occurring in the nucleoli. (+info)
Modification of resistance of mice to Naegleria fowleri infections.
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Naegleria fowleri, which produces a fatal meningoencephalitis in humans, is also able to produce a progressive and fatal disease in mice. The course of the disease in DUB/ICR mice is dependent upon the infecting dose of organisms, whether administered intraperitoneally (i.p.) or intravenously (i.v.). All of the mice receiving 10(7) trophozoites/mouse i.v. or 4.85 X 10(7) trophozoites/mouse i.p. were killed within 10 days. Escherichia coli O26:B6 lipopolysaccharide, administered at a dose of 1 mg/kg 24 h prior to N. fowleri, afforded some protection for several days after challenge, but by day 8 there was no difference in survival of untreated and endotoxin-treated mice. No significant protection was afforded by a complex of lipid A with concanavalin A (ConA) or bovine serum albumin (BSA) or by dimethylmyristamide-BSA, dimethylmyristamide, BSA, beta-hydroxymyristic acid-ConA, beta-hydroxymyristic acid, ConA, myristic acid-BSA, or myristic acid. Mice surviving primary i.v. or i.p. challenge doses of N. fowleri, 5 X 10(6) and 10(7) trophozoites/mouse, respectively, were highly resistant to rechallenge with an i.v. dose of organisms (5 X 10(6) Naegleria/mouse) that produced uniformly fatal disease in untreated control mice. (+info)
Lipophosphonoglycan of the plasma membrane of A canthamoeba castellanii. Inositol and phytosphingosine content and general structural features.
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Lipophosphonoglycan, a major component of the plasma membrane of Acanthamoeba castellanii, has now been shown to contain 8% inositol and 13% C25- and C24-phytosphingosines in addition to the previously identified content of neutral sugars (26%), amino sugars (3%), aminophosphonates (10%), acidhydrolyzable phosphate (3%), and long chain fatty acids (14%). The fatty acids and phytosphingosines are in ceramide groups. Lipophosphonoglycan can be separated by dodecyl sulfate-polyacrylamide electrophoresis into two major components that are similar in composition except for different oligosaccharide groups. A tentative structural model incorporating these features is proposed in which each of the two components of lipophosphonoglycan is conceived as an oligomeric inositol-containing glycosphingolipid. (+info)
Inhibition of cell division in amoebae: the incorporation of tritiated precursors into Amoeba proteus after the injection of non-homologous cytoplasm.
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The injection of non-homologous cytoplasm into any strain of large free-living amoebae leads to a 60% inhibition of division amongst recipient cells. When the post-microsomal supernatant fraction of Amoeba discoides was injected into A. proteus, this inhibition of division was as high as 95%. The incorporation of tritiated precursors, either [3H]uridine or 3H-amino acids, into these inhibited amoebae was studied at various times after the injection of the inhibitory material using autoradiography. When cells were grown in [3H]uridine, autoradiographs indicated that RNA synthesis had ceased 2 days after the injection of non-homologous material. However, if [3H]uridine was injected into the inhibited cells, some synthesis of RNA could be detected up to 4 days after the injection of inhibitor. These results suggested that uptake of [3H]uridine was impaired and that one site of action of the inhibitory molecules was RNA synthesis for membrane components. Experiments with a variety of 3H-amino acids suggested that protein synthesis continued for at least 9 days after the injection of non-homologous cytoplasm, and that in these cells some informational RNA molecules were long-lived. There seemed to be accumulation of material containing [3H]lysine in the nuclei of control cells taken at random from cultures, and this was seen in the nuclei of inhibited cells 1 day after injection. However, 2 days after the injection of inhibitor, no accumulation of [3H]lysine-containing material was found in the nuclei. (+info)
Developmentally regulated usage of Physarum DNA replication origins.
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To determine the extent to which eukaryotic replication origins are developmentally regulated in transcriptionally competent cells, we compared origin use in untreated growing amoebae and plasmodia of Physarum polycephalum. At loci that contain genes transcribed in both developmental stages, such as the ribosomal RNA genes and two unlinked actin genes, we show that there is a similar replicational organization, with the same origins used with comparable efficiencies, as shown by two-dimensional agarose-gel electrophoresis. By contrast, we found cell-type-specific replication patterns for the homologous, unlinked profilin A (proA) and profilin P (proP) genes. proA is replicated from a promoter-proximal origin in amoebae, in which it is highly expressed, and is replicated passively in the plasmodium, in which it is not expressed. Conversely, proP is replicated passively and is not expressed in amoebae, but coincides with an efficient origin when highly expressed in the plasmodium. Our results show a reprogramming of S phase that is linked to the reprogramming of transcription during Physarum cell differentiation. This is achieved by the use of two classes of promoter-associated replication origins: those that are constitutively active and those that are developmentally regulated. This suggests that replication origins, like genes, are under epigenetic control associated with cellular differentiation. (+info)
Environmental isolation of Balamuthia mandrillaris associated with a case of amebic encephalitis.
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This report describes the first isolation of the ameba Balamuthia mandrillaris from an environmental soil sample associated with a fatal case of amebic encephalitis in a northern California child. Isolation of the ameba into culture from autopsied brain tissue confirmed the presence of Balamuthia: In trying to locate a possible source of infection, soil and water samples from the child's home and play areas were examined for the presence of Balamuthia: The environmental samples (plated onto nonnutrient agar with Escherichia coli as a food source) contained, in addition to the ameba, a variety of soil organisms, including other amebas, ciliates, fungi, and nematodes, as contaminants. Presumptive Balamuthia amebas were recognized only after cultures had been kept for several weeks, after they had burrowed into the agar. These were transferred through a succession of nonnutrient agar plates to eliminate fungal and other contaminants. In subsequent transfers, axenic Naegleria amebas and, later, tissue cultures (monkey kidney cells) served as the food source. Finally, the amebas were transferred to cell-free axenic medium. In vitro, the Balamuthia isolate is a slow-growing organism with a generation time of approximately 30 h and produces populations of approximately 2 x 10(5) amebas per ml. It was confirmed as Balamuthia by indirect immunofluorescence staining with rabbit anti-Balamuthia serum and human anti-Balamuthia antibody-containing serum from the amebic encephalitis patient. The environmental isolate is similar in its antimicrobial sensitivities and identical in its 16S ribosomal DNA sequences to the Balamuthia isolate from the deceased patient. (+info)
Molecular characterisation of Neoparamoeba strains isolated from gills of Scophthalmus maximus.
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Small subunit ribosomal RNA gene sequences were determined for 5 amoeba strains of the genus Neoparamoeba Page, 1987 that were isolated from gills of Scophthalmus maximus (Linnaeus, 1758). Phylogenetic analyses revealed that 2 of 5 morphologically indistinguishable strains clustered with 6 strains identified previously as N. pemaquidensis (Page, 1970). Three strains branched as a clade separated from N. pemaquidenis and N. aestuarina (Page, 1970) clades. Our analyses suggest that these 3 strains could be representatives of an independent species. In a more comprehensive eukaryotic tree, strains belonging to Neoparamoeba spp. formed a monophyletic group with a sister-group relationship to Vannella anglica Page, 1980. They did not cluster with Gymnamoebae of the families Hartmannellidae, Flabellulidae, Leptomyxidae or Amoebidae presently available in GenBank. (+info)