PubMed Health⌕ Search

Biomedical subjects

D R Coombe

Publications and source records attributed to D R Coombe.

28 records · Page 2Linked to original sources
PubMed1991

Isolation and characterization of cell adhesion molecules from the marine sponge, Ophlitaspongia tenuis.

Previous studies suggested that cell adhesion in the marine sponge, Ophlitaspongia tenuis, is mediated by a 35 kDa cell surface protein which interacts with an extracellular sulfated polysaccharide. This paper describes a simple and efficient procedure for isolating both putative cell adhesion molecules from detergent lysates of O. tenuis cells, the procedure being based on the fortuitous affinity of the sponge polysaccharide for heparin. The purified polysaccharide inhibits O. tenuis sponge cell aggregation, is highly sulfated and represents a glycosaminoglycan containing glucuronic acid. N-sulfated glucosamine and, possibly, glucose. The purified 35 kDa protein has a high affinity for the sponge polysaccharide and also, selectively interacts with dextran sulfate, a polysaccharide that has been shown previously to both bind to the sponge cell surface and inhibit aggregation of O. tenuis cells. Collectively, the data supports the hypothesis that the 35 kDa molecule is the major cell adhesion protein in O. tenuis. Preliminary data also suggests that the sponge contains an endogenous glycan hydrolase which can cleave the sponge polysaccharide.

Animals↗
PubMed1987

Evidence that sulphated polysaccharides inhibit tumour metastasis by blocking tumour-cell-derived heparanases.

Recent studies in this laboratory demonstrated that several sulphated polysaccharides can inhibit metastasis of the rat mammary adenocarcinoma 13762 MAT, probably by preventing the passage of tumour cells through the walls of blood vessels. In order to directly test this possibility, 13762 MAT cells were cultured with (35S)O4(=)-labelled subendothelial extracellular matrices (ECM) and ECM degradation was monitored in either the presence or absence of different sulphated polysaccharides. Degradation products were detected by sodium dodecyl sulphate polyacrylamide gel electrophoresis and subsequent autoradiography. The 5 sulphated polysaccharides that had previously been shown to possess anti-metastatic activity were potent inhibitors of the degradation of subendothelial ECM by 13762 MAT cells. In contrast, of the 4 polysaccharides tested that failed to inhibit metastasis, 3 had no effect on ECM breakdown and one (carrageenan-kappa) was substantially less effective at inhibiting ECM degradation than the anti-metastatic preparations. It was also shown that 13762 MAT cells produce a heparan sulphate-specific glycosidase (heparanase) that degrades the heparan sulphate side-chains of the ECM, the action of this enzyme rather than that of other ECM-solubilizing enzymes being inhibited by the antimetastatic sulphated polysaccharides. Additional experiments indicated that the anti-coagulant activity of the polysaccharides probably plays a minor role in their anti-metastatic effects since heparin, almost completely depleted (98-99.5%) of heparin molecules with anti-coagulant activity by passage over an anti-thrombin III column, retained its ability to inhibit 13762 MAT heparanases and was almost as effective as unfractionated heparin at inhibiting tumour-cell metastasis. Collectively, these data suggest that sulphated polysaccharides inhibit the metastasis of 13762 MAT cells by inhibiting tumour-cell-derived heparanases involved in the penetration of the vascular endothelium and its underlying basement membrane by tumour cells.

Animals↗
PubMed1987

Analysis of the inhibition of tumour metastasis by sulphated polysaccharides.

Lung metastases resulting from the intravenous (i.v.) injection of cells from the rat mammary adenocarcinoma 13762 MAT were significantly reduced by a variety of sulphated polysaccharides, the most effective being heparin, fucoidan and Carrageenan lambda. Although all the inhibitory polysaccharides were anticoagulants, it is unlikely that anticoagulation is the total explanation of their antimetastatic effect because: (i) heparin preparations from 2 different suppliers, although exhibiting comparable anticoagulant activities, differed 10-fold in their antimetastatic capability; (ii) certain sulphated polysaccharides consistently gave a 30% difference in the number of metastatic lesions, yet exhibited identical anticoagulant activity; and (iii) the entrapment of 13762 MAT cells in the lung was not impaired by heparin or fucoidan. It was more probable that the sulphated polysaccharides were interfering with the passaging of tumour cells across the capillary wall as heparin significantly inhibited metastasis when injected up to 3 hr after lodgement, and heparin and fucoidan caused a gradual loss of tumour cells from the lung which only became apparent greater than 1 hr following cell lodgement. The data did not eliminate the possibility that tumour cell adhesion to the endothelium occurred via sulphated polysaccharide recognition. A negative correlation existed between the sulphated polysaccharides that bound to the surface of the tumour cells and those that inhibited metastasis.

Animals↗
PubMed1987

A role for sulfated polysaccharide recognition in sponge cell aggregation.

Molecules binding sulfated polysaccharides were detected as lectins in cholate lysates of cells from twelve sponge species. Each species exhibited a unique binding profile. The pattern of binding indicated that the specificity was most probably determined by the orientation of the sulfate groups on the polysaccharide chains. Cells from each of the three species examined in more detail were found to express sulfated polysaccharide-binding molecules at their surface and at least one of the polysaccharides recognized was found to inhibit the reaggregation of cells from each species. Moreover, in all but one instance, lectins for the inhibitory polysaccharide were both detected in cell lysates and shown to be expressed at the cell surface. Sulfated polysaccharides, therefore, appeared to be involved in cell interaction events in the Porifera. This conclusion was confirmed by the isolation via ion exchange chromatography of an endogenous polysaccharide from an O. tenuis cell extract. This molecule contained uronic acid and hexose units in a ratio of 2:1, 11.9% sulfur and less than 0.5% protein. It inhibited the aggregation of O. tenuis cells and the agglutination of dextran-sulfate- and polyvinyl-sulfate-coupled erythrocytes by O. tenuis cell lysates. O. tenuis cell aggregation was also inhibited by polyvinyl sulfate and dextran sulfate and molecules binding these compounds were expressed on the surface of O. tenuis cells. Thus, is was probable that the cell surface receptor for polyvinyl sulfate and dextran sulfate and isolated sponge sulfated polysaccharide are one and the same. Finally, using a dextran sulfate affinity procedure, a 35 kD dextran-sulfate-binding protein was isolated from the surface of O. tenuis cells. The possibility that the polysaccharide isolated from O. tenuis cell extracts in the absence of calcium is the monomeric form of a cell aggregation-enhancing factor is discussed.

Animals↗
PubMed1987

Evidence that the cytoskeleton plays a key role in cell adhesion.

A range of pharmacological agents with defined effects on cell metabolism was used to determine the metabolic requirements of three cell adhesion systems: aggregation of cells from the sponge, Ophlitaspongia tenuis; fibronectin-induced adhesion of fibroblasts to substrata and an in vitro murine thymocyte-macrophage interaction. Cell adhesion in all three systems was found to have similar metabolic requirements, implying that the mechanism of cell adhesion has been conserved through evolution. In fact, based on analysis of F-actin organization in fibroblasts, all of the pharmacological agents that inhibited cell adhesion were found to disrupt the cytoskeleton, suggesting that the cytoskeleton plays a central role in the adhesion process, presumably via redistribution of cell surface molecules. This concept was supported by the finding that the same drugs that inhibited cell adhesion inhibited anti-Ig-induced redistribution of surface Ig on B lymphocytes. The drug inhibition studies also revealed that two drugs, bromophenacyl bromide (BPB) and nordihydroguaiaretic acid (NDGA), that were previously believed to be selective inhibitors of arachidonic acid synthesis and metabolism, are also potent disruptors of the cytoskeleton.

Acetophenones↗
PubMed1986

Fc receptor-independent phagocytosis by mouse macrophages of erythrocytes sensitized with a lectin from a marine invertebrate.

A lactose-specific lectin present in the haemolymph of the colonial ascidian Botrylloides leachii was tested for its ability to act as an opsonin for the phagocytosis of erythrocytes by mouse macrophages. Sensitization of sheep or mouse erythrocytes with one agglutinating dose of the invertebrate agglutinin enhanced significantly the clearance of these cells from the circulation of mice, as did treatment with specific antibody. By measuring the adhesion and phagocytosis of 51Cr-labelled erythrocytes by monolayers of macrophages in vitro, it was shown that the B. leachii agglutinin was highly opsonic, promoting the ingestion of erythrocytes by the macrophages with an initial efficiency similar to that of specific antibody. The adherence and ingestion of antibody-coated erythrocytes was severely inhibited by blocking Fc receptors on the macrophages with soluble immune complexes, whereas the binding and ingestion of lectin-coated erythrocytes was unaffected by this treatment. The results demonstrate that invertebrate lectins can act as efficient opsonins for the uptake of particles by vertebrate phagocytes and that it is not necessary for particles to bind to Fc receptors for phagocytosis to be induced.

Animals↗
PubMed1982

Identification of the HA-2 agglutinin in the haemolymph of the ascidian Botrylloides leachii as the factor promoting adhesion of sheep erythrocytes to mouse macrophages.

The HA-2 agglutinin purified from B. leachii haemolymph is shown to mediate the binding of sheep erythrocytes to mouse macrophages. This agglutinin appears to be wholly responsible for the adhesive activity of haemolymph, since upon chromatography of the latter through Sephadex G-200, the adhesive activity for both sheep and guinea pig erythrocytes was confined to those fractions containing the HA-2 agglutinin. The HA-1 agglutinin recovered in earlier fractions was unable to promote the adhesion of guinea pig erythrocytes to macrophages. Adsorption experiments indicated that this was due to a lack of ligand sites on the macrophage surface. These data support earlier conclusions that the HA-1 and HA-2 agglutinins have distinct binding specificities.

Animals↗
PubMed1982

Haemagglutinin levels in haemolymph from the colonial ascidian Botrylloides leachii following injection with sheep or chicken erythrocytes.

Haemolymph was collected from colonies of Botrylloides leachii killed at various times after injection with sheep or chicken erythrocytes and the agglutination titre for sheep, chicken and guinea-pig erythrocytes was determined. Controls included haemolymph from groups of uninjected colonies and from others injected with balanced salt solution. Animals given a single injection of erythrocytes exhibited no change in titre until the second week when a marginal (2- to 4-fold) but statistically significant rise in titre was detected using each of the 3 types of indicator erythrocytes. A return to control values was observed by 6 weeks. The response to a second injection of erythrocytes, given 6 weeks after the first, appeared to be identical in magnitude and time of onset to the primary response, i.e. there was no indication of an anamnestic response. The increased haemagglutinating activity apparent 2 weeks after each injection was attributable to a rise in the HA-2 agglutinin specifically, since the activity of the HA-1 agglutinin (a calcium-dependent lectin which binds to guinea-pig erythrocytes only) remained unchanged. The results are considered in relation to self: non-self recognition in this species.

Animals↗
PubMed1981

An agglutinin in the haemolymph of an ascidian promoting adhesion of sheep erythrocytes to mouse macrophages.

Sheep erythrocytes sensitized with subagglutinating doses of haemolymph from Botrylloides leachii were found to bind strongly to mouse peritoneal macrophages in vitro. Erythrocytes sensitized with similar agglutinating doses of plant lectins or haemolymph from the fresh water crayfish Cherax destructor did not adhere. The adherence promoted by B. leachii haemolymph appears to be a heteroagglutination reaction mediated by a molecule which binds to lactose-like determinants on both erythrocytes and macrophages.

Animals↗