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排序方式: 共有185条查询结果,搜索用时 15 毫秒
1.
2.
Differential expression of metastasis-associated cell surface glycoproteins and mRNA in a murine large cell lymphoma 总被引:1,自引:0,他引:1
G L Nicolson R A LaBiche M L Frazier M Blick R J Tressler C L Reading T Irimura V Rotter 《Journal of cellular biochemistry》1986,31(4):305-312
A metastatic variant cell subline of the Abelson virus-transformed murine large lymphoma/lymphosarcoma RAW117 has been selected in vivo ten times for liver colonization. Highly metastatic subline RAW117-H10 forms greater than 200 times as many gross surface liver tumor nodules as the parental line RAW117-P. Analysis of cellular proteins and glycoproteins indicates reduced expression of murine Moloney leukemia virus-associated p15, p30, and gp70, and increased expression of a sialoglycoprotein, gp150, in the highly metastatic H10 cells. Northern analyses of oncogene expression suggested that mRNA of various oncogenes was expressed equally or not expressed in the RAW117 cells of differing metastatic potential. Differential gene expression was examined using a cDNA library of 17,600 clones established from poly A+ mRNA isolated from H10 cells. The cDNA library was screened by the colony hybridization technique using probes made from both RAW117-P and -H10 cells. Approximately 99.5% of these cDNA clones were expressed identically in P and H10 cells. Of the few differentially expressed cDNA clones (approx. 150/17,600), one-half of these were identified as Moloney leukemia virus sequences in a separate probing with a radiolabeled Moloney leukemia virus probe. The remainder of the differentially expressed mRNA detected by colony hybridization of the cDNA library were expressed at higher levels (approx. 1/6) or lower levels (approx. 1/3) in the highly metastatic H10 cells. 相似文献
3.
The β-lactamase from Klebsiella pneumoniae E70 behaved in a similar fashion to the TEM-2 plasmid mediated enzyme on reaction with clavulanic acid. Both enzymes produced two types of enzyme–clavulanate complex, a transiently stable species (t½=4min at pH7.3 and 37°C) and irreversibly inhibited enzyme. In the initial rapid reaction (2.5min) the enzymes partitioned between the transient and irreversible complexes in the ratios 3:1 for TEM-2 β-lactamase and 1:1 for Klebsiella β-lactamase. Biphasic inactivation was observed for both enzymes and the slower second phase was rate limited by the decay of the transiently stable complex. This decay released free enzyme for further reaction with fresh clavulanic acid, the products again partitioning between transiently stable and irreversibly inhibited enzyme. This cycle continued until all the enzyme had been irreversibly inhibited. A 115 molar excess of inhibitor was required to achieve complete inactivation of TEM-2 β-lactamase. Hydrolysis of clavulanic acid with product release appeared to occur with the inhibition reaction, which explained this degree of clavulanic acid turnover. The stoichiometry of the interaction with Klebsiella β-lactamase was not examined. The penicillinase from Proteus mirabilis C889 was rapidly inhibited by low concentrations of clavulanic acid. The major product was a moderately stable complex (t½=40min at pH7.3 and 37°C); the proportion of the enzyme that was irreversibly inactivated was small. The cephalosporinase from Enterobacter cloacae P99 had low affinity for the inhibitor and only reacted with high concentrations of clavulanic acid (k=4.0m−1·s−1) to produce a relatively stable complex (t½=180min at pH7.3 and 37°C). No irreversible inactivation of this enzyme was detected. The rates of decay of the clavulanate–enzyme complexes produced in reactions with Proteus and Enterobacter enzymes were markedly increased at acid pH. 相似文献
4.
AB Kane RP Stanton EG Raymond ME Dobson ME Knafelc JL Farber 《The Journal of cell biology》1980,87(3):643-651
The relationship between intracellular lysosomal rupture and cell death caused by silica was studied in P388d(1) macrophages. After 3 h of exposure to 150 μg silica in medium containing 1.8 mM Ca(2+), 60 percent of the cells were unable to exclude trypan blue. In the absence of extracellular Ca(2+), however, all of the cells remained viable. Phagocytosis of silica particles occurred to the same extent in the presence or absence of Ca(2+). The percentage of P388D(1) cells killed by silica depended on the dose and the concentration of Ca(2+) in the medium. Intracellular lyosomal rupture after exposure to silica was measured by acridine orange fluorescence or histochemical assay of horseradish peroxidase. With either assay, 60 percent of the cells exposed to 150 μg silica for 3 h in the presence of Ca(2+) showed intracellular lysosomal rupture, was not associated with measureable degradation of total DNA, RNA, protein, or phospholipids or accelerated turnover of exogenous horseradish peroxidase. Pretreatment with promethazine (20 μg/ml) protected 80 percent of P388D(1) macrophages against silica toxicity although lysosomal rupture occurred in 60-70 percent of the cells. Intracellular lysosomal rupture was prevented in 80 percent of the cells by pretreatment with indomethacin (5 x 10(-5)M), yet 40-50 percent of the cells died after 3 h of exposure to 150 μg silica in 1.8 mM extracellular Ca(2+). The calcium ionophore A23187 also caused intracellular lysosomal rupture in 90-98 percent of the cells treated for 1 h in either the presence or absence of extracellular Ca(2+). With the addition of 1.8 mM Ca(2+), 80 percent of the cells was killed after 3 h, whereas all of the cells remained viable in the absence of Ca(2+). These experiments suggest that intracellular lysosomal rupture is not causally related to the cell death cause by silica or . Cell death is dependent on extracellular Ca(2+) and may be mediated by an influx of these ions across the plasma membrane permeability barrier damaged directly by exposure to these toxins. A23187相似文献
5.
Clavulanic acid inhibited both the extracellular and cell-extract beta-lactamases of the four Staphylococcus aureus strains tested. The inhibition of S. aureus Russell cell-extract enzyme appeared to be active-site-directed and proceeded in a first-order fashion consistent with the formation of a covalent intermediate. Inhibited enzyme free of excess clavulanic acid was shown to regenerate enzyme activity slowly at pH 7.0, but the rate of reactivation increased at acid pH. When the enzyme was incubated with excess clavulanic acid complete inhibition was rapidly obtained, during further incubation clavulanic acid was shown to disappear slowly and complete loss of clavulanic acid from the reaction mixture coincided with the onset of the return of enzyme activity. A reactive enamine resulting from enzymic hydrolysis of the beta-lactam ring of clavulanic acid has been proposed as a possible intermediate in the inhibitory mechanism. 相似文献
6.
Dr. D. G. Jones L. T. Ellison L. C. Reading M. M. Dittmer 《Cell and tissue research》1976,169(1):49-66
Summary Synapses of the oculomotor nucleus of Echidna have been examined ultrastructurally with the aim of integrating data obtained from osmicated and nonosmicated PTA stained material. Particular emphasis has been laid on the relationship between the synaptic vesicles of the osmicated material and the presynaptic network and vesicular grid of the PTA material. This relationship has been explored qualitatively by examining osmicated material of varying qualities of fixation. Such material contains dense projections in addition to synaptic vesicles, and various vesicular network appearances. A variety of measurement techniques have shown that the PTA network is characterised by reticular strands, spaces, and regular hexagonal units smaller than vesicles, these observations prompting the formulation of a vesicle-network coincidence model of the presynaptic terminal. This model has been tested by tracing the profiles of vesicles within the PTA network and comparing their size and shape frequency distributions with those of osmicated synaptic vesicles. The distributions have been found to be essentially similar, suggesting that vesicles can be located within the network, and that the hexagonal network units are formed only in the presence of an underlying vesicular matrix.Additionally, the following points have emerged: 1) the dense projections in the two types of material appear to be equivalent; 2) a loose correlation exists between dense projections and vesicles in osmicated terminals, increase in the area of the dense projections being associated with a decrease in the area of the vesicles; 3) network and dense projection units are similar. In view of the similarity between network and dense projection units, the demonstrated vesicular basis of the network raises the question of whether dense projections are entirely independent structures, or whether they depend in part for their existence on the nearby presence of synaptic vesicles.This work was supported by the Arnold Yeldham and Mary Raine Research Foundation of the University of Western Australia and by the Australian Research Grants Committee and the Nuffield Foundation 相似文献
7.
Londrigan SL Turville SG Tate MD Deng YM Brooks AG Reading PC 《Journal of virology》2011,85(6):2990-3000
It is widely recognized that sialic acid (SA) can mediate attachment of influenza virus to the cell surface, and yet the specific receptors that mediate virus entry are not known. For many viruses, a definitive demonstration of receptor function has been achieved when nonpermissive cells are rendered susceptible to infection following transfection of the gene encoding a putative receptor. For influenza virus, such approaches have been confounded by the abundance of SA on mammalian cells so that it has been difficult to identify cell lines that are not susceptible to infection. We examined influenza virus infection of Lec2 Chinese hamster ovary (CHO) cells, a mutant cell line deficient in SA. Lec2 CHO cells were resistant to influenza virus infection, and stable cell lines expressing either DC-SIGN or L-SIGN were generated to assess the potential of each molecule to function as SA-independent receptors for influenza A viruses. Virus strain BJx109 (H3N2) bound to Lec2 CHO cells expressing DC-SIGN or L-SIGN in a Ca(2+)-dependent manner, and transfected cells were susceptible to virus infection. Treatment of Lec2-DC-SIGN and Lec2-L-SIGN cells with mannan, but not bacterial neuraminidase, blocked infection, a finding consistent with SA-independent virus attachment and entry. Moreover, virus strain PR8 (H1N1) bears low levels of mannose-rich glycans and was inefficient at infecting Lec2 CHO cells expressing either DC-SIGN or L-SIGN, whereas other glycosylated H1N1 subtype viruses could infect cells efficiently. Together, these data indicate that human C-type lectins (DC-SIGN and L-SIGN) can mediate attachment and entry of influenza viruses independently of cell surface SA. 相似文献
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9.
Fernanda Ana-Sosa-Batiz Hillary Vanderven Sinthujan Jegaskanda Angus Johnston Steven Rockman Karen Laurie Ian Barr Patrick Reading Marit Lichtfuss Stephen J. Kent 《PloS one》2016,11(4)
BackgroundImmunity to human influenza A virus (IAV) infection is only partially understood. Broadly non-neutralizing antibodies may assist in reducing disease but have not been well characterized.MethodsWe measured internalization of opsonized, influenza protein-coated fluorescent beads and live IAV into a monocytic cell line to study antibody-dependent phagocytosis (ADP) against multiple influenza hemagglutinin (HA) subtypes. We analyzed influenza HA-specific ADP in healthy human donors, in preparations of intravenous immunoglobulin (IVIG), and following IAV infection of humans and macaques.ResultsWe found that both sera from healthy adults and IVIG preparations had broad ADP to multiple seasonal HA proteins and weak cross-reactive ADP to non-circulating HA proteins. The ADP in experimentally influenza-infected macaque plasma and naturally influenza-infected human sera mediated phagocytosis of both homologous and heterologous IAVs. Further, the IAV phagocytosed in an antibody-mediated manner had reduced infectivity in vitro.ConclusionWe conclude that IAV infections in humans and macaques leads to the development of influenza-specific ADP that can clear IAV infection in vitro. Repeated exposure of humans to multiple IAV infections likely leads to the development of ADP that is cross-reactive to strains not previously encountered. Further analyses of the protective capacity of broadly reactive influenza-specific ADP is warranted. 相似文献
10.
Removal of apex predators can drive ecological regime shifts owing to compensatory positive and negative population level responses by organisms at lower trophic levels. Despite evidence that apex predators can influence ecosystems though multiple ecological pathways, most studies investigating apex predators’ effects on ecosystems have considered just one pathway in isolation. Here, we provide evidence that lethal control of an apex predator, the dingo Canis dingo, drives shifts in the structure of Australia's tropical‐savannah ecosystems. We compared mammal assemblages and understorey structure at seven paired‐sites. Each site comprised an area where people poisoned dingoes and an area without dingo control. The effects of dingo control on mammals scaled with body size. Where dingoes were poisoned, we found greater activity of herbivorous macropods and feral cats, a mesopredator, but sparser understorey vegetation and lower abundances of native rodents. Our study suggests that ecological cascades arising from apex predators’ suppressive effects on herbivores and mesopredators occur simultaneously. Concordant effects of dingo removal across tropical‐savannah, forest and desert biomes suggest that dingoes once exerted ubiquitous top–down effects across Australia and provides support for calls that top–down forcing should be considered a fundamental process governing ecosystem structure. 相似文献