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At least 451 records · Page 25Linked to original sources
PubMed1996

Site-directed mutagenesis within an ectoplasmic ATPase consensus sequence abrogates the cell aggregating properties of the rat liver canalicular bile acid transporter/ecto-ATPase/cell CAM 105 and carcinoembryonic antigen.

Recent studies of the rat liver canalicular bile acid transporter/ecto-ATPase/cell CAM 105 (CBATP), a member of the carcinoembryonic antigen (CEA) supergene family, indicate that it is a multifunctional protein possessing bile acid efflux, ecto-ATPase, and intercellular aggregating properties. Cheung et al. (Cheung, P. H., Luo, W., Qiu, Y., Zhang, K. E., Millron, P., Lin, S. H. (1993) J. Biol. Chem. 268, 24303-24310) have shown that the amino-terminal Ig V-like domain of this protein is required for its aggregating properties, much like the homologous amino-terminal domain of CEA is required for its aggregating properties. The amino-terminal domains of both CBATP and CEA include a consensus ATPase sequence. Site-directed mutagenesis within this ATPase consensus sequence completely eliminates the ecto-ATPase activity of CBATP (Sippel, C. J., McCollum, M., Perlmutter, D. H. (1994) J. Biol. Chem. 269, 2820-2826). In this study we examined the possibility that it is this ATPase consensus sequence which is required for the cell aggregating properties of CBATP and CEA and whether there is a relationship between ATPase, aggregating, and bile acid efflux activities. For this we used a baculovirus vector to express in Sf9 cells wild type as well as mutant and chimeric CBATP and CEA molecules. The results indicate that Arg-98 in the ATPase consensus sequence of CBATP and the corresponding residue of CEA are essential for the aggregating properties of these molecules. Moreover Arg-98 is essential for CBATP to interact with itself, CEA to interact with itself, and CBATP to interact with CEA. However, the role of Arg-98 in aggregation is distinct from its role in ecto-ATPase activity and the aggregating properties cannot be attributed to a change in ATP metabolism in the pericellular milieu.

Adenosine Triphosphatases↗
PubMed1997

Moderate weight reduction improves red cell aggregation and factor VII activity in overweight subjects.

OBJECTIVE: To investigate the effect of a dietary intervention to reduce body weight on red cell aggregation (RCA), factor VII activity, plasminogen activator inhibitor (PAI) activity, tissue plasminogen activator (t-PA) antigen, fibrinogen, whole blood and plasma viscosity, haematocrit and lipids. DESIGN: Open single stranded study of dietary intervention for weight loss in a volunteer sample. SUBJECTS: Forty-five subjects whose BMI exceeded 26 kg/m2 were recruited and received dietetic advice designed to reduce body weight by 0.5 kg per week. MEASUREMENTS: Body weight and waist and hip circumferences, dietary intake by seven day weighed inventory, RCA, factor VII activity, PAI activity, t-PA antigen, fibrinogen, whole blood and plasma viscosity, haematocrit and lipids. RESULTS: After 12 weeks of dietary intervention there were reductions in body weight and BMI by 5.9 (s.d. 3.3) kg and 1.9 (s.d. 1.0) kg/m2 respectively in males, and 4.1 (s.d. 2.9) kg and 1.6 (s.d. 1.1) kg/m2 in females (P < 0.0001). Factor VII activity (P = 0.0043), RCA (P = 0.01) and t-PA antigen (P = 0.016) were reduced in females after weight reduction but no differences were found in PAI activity, whole blood, plasma viscosity or haematocrit. The changes in factor VII activity and RCA were appropriate for the changes in BMI on the basis of the relationships of the risk factors with BMI in a cross sectional survey of a representative Scottish population. Plasma total cholesterol was reduced (P = 0.016) but HDL cholesterol and triglycerides remained unchanged. There were significant associations between the reductions in factor VII activity and BMI (r = 0.395, P = 0.013) and between the reductions in RCA and waist to hip ratio (r = 0.350, P = 0.04). No relationship was seen between changes in serum cholesterol and changes in factor VII activity or RCA. CONCLUSIONS: Modest weight loss, of 5% body weight, with conventional dietary intervention reduces two established risk factors for ischaemic heart disease (factor VII activity and RCA) which are generally elevated in those with increased body weight.

Adult↗
PubMed2004

Squamous cell carcinoma cell aggregates escape suspension-induced, p53-mediated anoikis: fibronectin and integrin alphav mediate survival signals through focal adhesion kinase.

Resistance to anoikis, or apoptosis triggered by detachment from the extracellular matrix (ECM), lengthens the survival of malignant cells, facilitating reattachment and colonization of secondary sites. To examine the molecular mechanisms underlying resistance to anoikis in human oral squamous cell carcinoma (SCC) cells, we cultured human squamous carcinoma (HSC-3) cells in suspension on plates coated with poly-2-hydroxyethyl methacrylate, which blocks access to the ECM. Cells in suspension that formed multicellular aggregates had significantly lower levels of apoptosis than single cells. Aggregates, but not single cells, had high levels of fibronectin. Preincubation with a cyclic arginine-glycine-aspartic acid peptide or fibronectin-blocking antibody significantly increased anoikis. Single cells had markedly lower expression of the integrin alpha(v) receptor than aggregates. Blocking alpha(v) function with a blocking antibody or by transfection with an antisense oligonucleotide increased apoptosis and inhibited aggregation. In single cells but not aggregates, phosphorylation of the integrin-associated focal adhesion kinase (FAK) at tyrosine 397 was reduced, and p53 levels were increased. Apoptosis was increased by blocking FAK with an antisense oligonucleotide and reduced by blocking p53. These findings show that SCC cells escape suspension-induced anoikis by forming multicellular aggregates that avail themselves of fibronectin survival signals mediated by integrin alpha(v). Single cells in suspension that do not form aggregates undergo anoikis because of decreased FAK phosphorylation and increased p53 levels. Thus, SCC cells appear to use neighboring cells and the ECM molecule FN to promote the metastatic phenotype.

Animals↗
PubMed2005

Simple and efficient production of mice derived from embryonic stem cells aggregated with tetraploid embryos.

Six newly derived hybrid mouse embryonic stem (ES) cell lines and two inbred ES cell lines were tested for their ability to produce completely ES cell-derived mice by aggregation of ES cells with tetraploid embryos. Forty-five ES cell-tetraploid pups were generated from six hybrid ES cell lines and no pups from two inbred ES cell lines. These pups were found to have increased embryonic and placental weights than control mice. Twenty-two pups survived to adulthood and produced normal offsprings, and the other 23 pups died of several reasons including respiratory distress, abdomen ulcer-like symptoms, and foster failure. The 22 adult ES cell-tetraploid mice were completely ES cell-derived as judged by coat color and germline transmission, only two of them was found to have tetraploid component in liver, blood, and lung as analyzed by microsatellite loci. Our data suggested that genetic heterozygosity is a crucial factor for postnatal survival of ES cell-tetraploid mice, and tetraploid embryo aggregation using hybrid ES cells is a simple and efficient procedure for immediate generation of targeted mouse mutants from genetically modified ES cell clones, in contrast to the standard protocol, which involves the production of chimeras and several breeding steps.

Animals↗
PubMed1982

The metabolism and activation of polycyclic aromatic hydrocarbons in epithelial cell aggregates and fibroblasts prepared from rat mammary tissue.

The metabolism of 7,12-dimethylbenz[a]anthracene (DMBA), benzo[a]pyrene (BP) and benz[a]anthracene (BA) by epithelial cell aggregates and fibroblasts in culture has been investigated using mammary tissue obtained from female Wistar rats. The results show that: (a) both types of mammary cells metabolise all three hydrocarbons into ether- and water-soluble derivatives; (b) the patterns of metabolites produced by epithelial cells and fibroblasts are similar but that fibroblasts form more of the water-soluble materials; (c) the major dihydrodiols formed are the 8,9-dihydrodiols of BA and DMBA and the 7,8- and 9,10-dihydrodiols of BP; (d) all three hydrocarbons are metabolise to form products that bind covalently to protein but only the potent carcinogens BP and DMBA are metabolised to form derivatives that react covalently with DNA; and (e) the chromatographic profiles of the hydrocarbon-deoxyribonucleoside adducts formed in epithelial cells treated with either BP or DMBA are similar to those obtained in analogous experiment with fibroblasts.

9,10-Dimethyl-1,2-benzanthracene↗
PubMed1993

Homophilic binding of PTP mu, a receptor-type protein tyrosine phosphatase, can mediate cell-cell aggregation.

The receptor-like protein tyrosine phosphatase, PTPmu, displays structural similarity to cell-cell adhesion molecules of the immunoglobulin superfamily. We have investigated the ability of human PTPmu to function in such a capacity. Expression of PTPmu, with or without the PTPase domains, by recombinant baculovirus infection of Sf9 cells induced their aggregation. However, neither a chimeric form of PTPmu, containing the extracellular and transmembrane segments of the EGF receptor and the intracellular segment of PTPmu, nor the intracellular segment of PTPmu expressed as a soluble protein induced aggregation. PTPmu mediates aggregation via a homophilic mechanism, as judged by lack of incorporation of uninfected Sf9 cells into aggregates of PTPmu-expressing cells. Homophilic binding has been demonstrated between PTPmu-coated fluorescent beads (Covaspheres) and endogenously expressed PTPmu on MvLu cells. Additionally the PTPmu-coated beads specifically bound to a bacterially expressed glutathione-S-transferase fusion protein containing the extracellular segment of PTPmu (GST/PTPmu) adsorbed to petri dishes. Covaspheres coated with the GST/PTPmu fusion protein aggregated in vitro and also bound to PTPmu expressed endogenously on MvLu cells. These results suggest that the ligand for this transmembrane PTPase is another PTPmu molecule on an adjacent cell. Thus homophilic binding interactions may be an important component of the function of PTPmu in vivo.

Animals↗
PubMed1980

A twelve-channel automatic device for continuous recording of cell aggregation by measurement of small-angle light-scattering.

We describe here a 12-channel aggregometer, evolved from the instrument described by Beug & Gerisch in 1972, which records the course of aggregation or agglutination of cells or other particles by following the changes in light-scattering of the aggregating suspension. The instrument incorporates a simple memory system for condensing the data, introduces an improved cuvette design, and can be adjusted in its responsiveness to light-scattering by particles of different sizes. In our aggregometer, a vertical wheel in an opaque thermostatted chamber accommodates up to 12 cuvettes each containing a cell suspension and an air bubble. The constant rising of the bubble as the wheel rotates causes the stirring action which promotes aggregation. At a certain point in its rotational path, each cuvette is penetrated by a beam of light focused upon an absorbing beam stop centred in front of a photomultiplier tube. Particles suspended in the cuvette scatter a portion of the light beyond the beam stop into the photomultiplier tube to produce an electrical pulse proportional to the photon input. Collection of these pulses with the wheel in continuous motion avoids any disturbance of the course of aggregation. The pulses are routed to memory circuits for summation and eventual recording by a 12-channel printing potentiometer which automatically colour-codes and numbers each curve. The cuvettes consist of 2 glass microscope coverslips affixed with silicone grease over a hole in a thin, stainless steel blank. They are very durable and are easily dismantled and reassembled for cleaning. The coverslips are replaced after each use. The discoid chamber of our cuvette permits uniform circulation of the bubble, which in turn causes gentle stirring of the aggregating suspension at a rate that is a direct and continuous function of rev/min. Measurement of light-scattering at small angles (3--5.5 degrees) provides great sensitivity to the disappearance of single cells and progressively less sensitivity to the coalescence of aggregates of progressively larger size. The signal generated by the photomultipler tube decreases as aggregation proceeds. At 32 rev/min, one data point per channel, representing the sum (average) of 24 successive measurements, is printed every 45 s. In the course of a 60-min assay under standard conditions, up to 23040 individual readings can be automatically taken, summed and plotted. In a comparison of 8 identical samples run simultaneously, the printed values after 60 min agreed with a standard deviation of +/- 2%.

Animals↗
PubMed1993

Inhibition of LFA-1-dependent human B-cell aggregation induced by CD40 antibodies and interleukin-4 leads to decreased IgE synthesis.

Antibodies to CD40 have been shown to induce homotypic aggregation of human resting B cells and B-cell lines via an LFA-1-dependent mechanism. We show here that interleukin-4 (IL-4) is a strong potentiator of this process and stimulation of tonsillar B cells for 4 days with IL-4 and CD40 antibodies resulted in the formation of large, dense aggregates. Also in this case, aggregation appeared to be chiefly dependent on the activation of LFA-1, although the small clusters of cells remaining after blocking with LFA-1 antibodies suggest the involvement of another adhesion system(s). When testing the relationship between aggregation and IgE synthesis, a known consequences of IL-4/CD40 stimulation, IgE levels were found to be significantly decreased in the presence of LFA-1 antibodies. In contrast to these observations, proliferation occurring in response to the IL-4/CD40 stimulation was not inhibitable by LFA-1 antibodies. Rather, in most cases, this was slightly enhanced, suggesting that aggregation may have a limiting effect on cell growth. Isolated aggregates, each of which could comprise more than 10(5) cells, were also examined by electron microscopy. This revealed a tissue-like structure of the aggregates with large contact areas and with minimal intercellular space between the adjacent cells. As the apparent inhibitory effect of aggregation on proliferation may reflect a negative autocrine signalling, which is enhanced by the close cell contact, we also tested the effect of neutralizing antibodies to IL-6, one of the factors known to be produced in the system. Such treatment did not affect aggregation but in most experiments enhanced proliferation. The results suggest that a possible effect of aggregation may be to enhance differentiation of cells and that this may also be associated with the difficulties in growing B cells in vitro.

Antibodies, Monoclonal↗
PubMed1998

Species-specific association of the cell-aggregation molecule mediates recognition in marine sponges.

Reaggregation of dissociated cells of marine sponges, resulting in reformation of functional sponges, is a calcium-dependent process mediated by large, proteoglycan-like molecules termed aggregation factors (AF). During aggregation, species-specific sorting of cells is often observed. We purified and characterized AFs from three different sponge species and investigated their role in species-specific aggregation using novel approaches. The calcium-dependent association between purified AFs is species-specific in most combinations, as was shown in overlay assays and bead-sorting assays with AFs immobilized onto colored beads. Species-specific interactions of living cells and AF-beads resulted in incorporation of only homospecific AF-beads into reforming cell aggregates. Sequences from peptides obtained from the AF core proteins could all be aligned to the sequence of one species, the Microciona prolifera AFp3 core protein. In contrast to this similarity, major species-specific differences were seen in carbohydrate composition and in the response of AFs to specific carbohydrate-recognizing antibodies. In summary, our data point to a prominent role for the calcium-dependent association of AFs in recognition processes during aggregation. As this association of AFs occurs via carbohydrate-carbohydrate interactions, we speculate that the specificity of those interactions may be fundamental to recognition mechanisms required for regeneration of individuals from dissociated cells and for rejection of foreign material by sponge individuals.

Animals↗
PubMed1997

Effect of mercuric ions on human erythrocytes. Relationships between hypotonic swelling and cell aggregation.

This study was undertaken to verify the hypothesis that the haemolytic effect of mercuric ions on human erythrocytes is strongly decreased under swelling conditions (relative to isotonic suspensions). In fact, interaction of Hg2+ with swollen erythrocytes yields a rapid and cooperative cell aggregation, a phenomenon that appears to prevent penetration of mercuric ions into the cells and, accordingly, to avoid any haemolytic effect induced by the Hg2+ entrance. Since in vivo erythrocytes undergo big shape changes (swelling being a kind of shape modification) related to mechanical or (in some animals) osmotic stresses, the reported observations turn out to be also of some relevance for the understanding of certain toxicological effects of mercuric ions.

4-Chloromercuribenzenesulfonate↗
PubMed1996

[Changes in red blood cell aggregation rate after aneurysmal subarachnoid hemorrhage].

Red blood cell (RBC) aggregability is one of the important factors determining blood viscosity in the microcirculation. The RBC aggregation rate was monitored in 38 patients who underwent early aneurysmal clipping surgery after subarachnoid hemorrhage (SAH). The intravascular factors (hematocrit, serum albumin, alpha 2-macroglobulin, fibrinogen, IgG) that influence RBC aggregation were also examined. The RBC aggregation rate increased on days 5-7 but decreased significantly as a result of hypervolemic hemodilution therapy (H-H therapy). The hematocrit level was also reduced by H-H therapy. The serum albumin concentration decreased and the serum alpha 2-macroglobulin concentration increased significantly on days 5-7. After H-H therapy, the serum albumin concentration increased and the serum alpha 2-macroglobulin concentration decreased significantly. Serum IgG and plasma fibrinogen concentrations did not change significantly. It is known that albumin decreases and alpha 2-macroglobulin increases RBC aggregability. It has become apparent that serum albumin and alpha 2-macroglobulin play important roles in the determination of RBC aggregability after SAH. We conclude that the improvement in RBC aggregability induced by H-H therapy is effective for reversing progressive neurological deterioration due to cerebral vasospasm.

Adult↗