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Biomedical subjects

M M Burger

Publications and source records attributed to M M Burger.

At least 109 records · Page 6Linked to original sources
PubMed1983

Fibronectin and laminin in the extracellular matrix and basement membrane of sea urchin embryos.

Fibronectin and laminin have been found in the extracellular matrix and in the basement membrane of sea urchin embryos during early development. These glycoproteins are also found on the cell surfaces of the outer epithelial layer and on the secondary mesenchyme cells within the blastocoel. The similarity of functions of the extracellular matrix and basement membrane is discussed, as is the similarity of their molecular components. These observations suggest the possibility that fibronectin and laminin form a continuous matrix surrounding the cells which links the outer ECM (hyaline layer) to the inner ECM (basement membrane). Such a network could coordinate the various activities of the embryo during early morphogenesis.

Animals↗
PubMed1982

Cell binding fragments from a sponge proteoglycan-like aggregation factor.

The marine sponge Microciona prolifera aggregation factor (MAF) is a 2 X 10(7) dalton proteoglycan. MAF mediates species-specific cell-cell recognition through two functionally different sites: a Ca2+-independent species-specific cell binding site and a Ca2+-dependent MAF-MAF binding site. Dissociation procedures combined with protease treatment were used to produce cell-binding pieces from the large complex. The seven different sized fragments produced were all uronic acid-rich glycoproteins of the apparent molecular weights: 15 X 10(6), 2.5 X 10(5), 1.2 X 10(5), 7 X 10(4), 2.7 X 10(4), 5 X 10(3), and 3.6 X 10(3). Each of the fragments retained species-specific binding to Microciona cells and was also capable of inhibiting MAF-promoted cell aggregation. However, the fragments were unable to bind to MAF-conjugated agarose beads in the presence or absence of CA2+ ions. These three properties are those expected for the cell binding site of MAF. Since the binding affinity decreased linearly with decreasing molecular weight of the fragments, we believe that the cell binding sites in MAF may be highly polyvalent, although to fully support such a concept, a detailed chemical characterization of each of the fragments is needed. A high valency of cell binding sites would overcome a relatively low Ka for the single site and would thereby not only guarantee specificity but also explain the need for the large size of the proteoglycan complex found to mediate species-specific sponge aggregation.

Animals↗
PubMed1982

Lectin-resistant variants of mouse melanoma cells. I. Altered metastasizing capacity and tumorigenicity.

From C57BL mouse melanoma B-16 cells, variant clones were selected in vitro which were resistant to the lectins wheat-germ agglutinin and ricin. Cells were also selected which survived toxic concentrations of concanavalin A. Four different in vivo assays using intradermal, intravenous, intraperitoneal and intramuscular injections were used to assess the tumorigenicity and metastasizing capacity of these lectin-resistant variants. It was concluded that to obtain a complete picture of the malignant properties of a given cell line or clone, all four assays have to be carried out. In comparison with the parental cells, the WGA-resistant cells showed a most dramatic decrease in metastasizing capacity through both lymphatic and vascular channels. Tumorigenicity was also reduced. The ricin-resistant cells showed a defective development into lung tumors and thus displayed a reduction in metastasis through the hematogenous route. Since this line did not change its capacity to metastasize via the lymphatic route, and the tumorigenicity was not significantly altered, it will be a good model for studies seeking to dissociate these two properties. The Con-A-selected cells, when injected intravenously, developed tumor nodules in the liver in addition to those in the lungs, while no striking alterations in tumorigenicity or metastasizing capacity could be detected in this line.

Animals↗
PubMed1982

The influence of membrane mutations on metastasis.

In an effort to assess the effect of surface carbohydrates upon the metastasizing properties of tumor cells, lectin-resistant mouse melanoma cells were selected. Wheat-germ-agglutinin-resistant lines displayed mainly decreased metastasis properties as well as well-defined alterations in surface carbohydrates: in a glycopeptide with four side chains, two of them were missing their terminal sialic acid residues while two fucoses were newly attached to the oligosaccharide. The enzymatic defect could be pinpointed to an over-60-fold increase in fucosyltransferase, while the sialyltransferase did not decrease significantly. Revertants were again selected with lectins and their fucosyltransferase activities returned to normal values again. The metastasizing potential of the revertants was not yet assessed carefully but a return of some of the metastasizing potential was noted.

Animals↗
PubMed1982

alpha-Actinin interacts specifically with model membranes containing glycerides and fatty acids.

A method was developed to identify specific protein-lipid interactions of complex lipid mixtures and to assess their effect upon the arrangement of such complexes in monolayers at an air-water interface. Its application to striated muscle alpha-actinin revealed that just two lipids selectively interact with alpha-actinin. One molecule of glyceride and one molecule of fatty acid were found to be associated in a constant stoichiometry with one molecule of the alpha-actinin dimer. In the presence of both glycerides and fatty acids unexpectedly rigid monolayer areas formed. This lipid specificity could be confirmed by brief protease digestion of alpha-actinin liposome mixtures followed by peptide analysis; the peptide patterns of alpha-actinin depended on the presence or absence of only these two lipids. Possible implications of these findings are discussed in the context of Z-line formation.

Actinin↗
PubMed1982

Enzymatic basis for a lectin-resistant phenotype: increase in a fucosyltransferase in mouse melanoma cells.

In the search for the biochemical basis of the control of glycosylation of cell surface carbohydrates, revertant clones were isolated from previously characterized wheat germ agglutinin-resistant clones of B16 mouse melanoma cells by selection for resistance to Lotus tetragonolobus lectin or to ricin. Comparison of the wheat germ agglutinin-resistant clones with the parent and revertant clones indicated that this phenotype was correlated with an increased sensitivity to the Lotus lectin, a 60- to 70-fold increase in alpha 1 leads to 3 fucosyltransferase activity and a decreased sialic acid content of the N-glycosidic chains of glycoproteins. The results suggest a novel type of control mechanism for lectin resistance, an increase in a glycosyltransferase activity. The presence of alpha 1 leads to 3 bound fucose on N-acetylglucosamine residues would interfere with the addition of sialic acid by alpha 2 leads to 3 linkages to galactose residues in the carbohydrate units, and this change could explain the resistance to wheat germ agglutinin and the increased sensitivity to the Lotus lectin. A change in a regulatory gene for the fucosyltransferase as a possible primary cause for the changed phenotype is discussed.

Animals↗
PubMed1981

The contribution of the calcium-dependent interaction of aggregation factor molecules to recognition: a system providing additional specificity forces?

Cells from the sponge Microciona prolifera display on their surfaces large but defined proteoglycan complexes (Microciona aggregation factor = MAF) that mediate species-specific cell aggregation by a process requiring high calcium ion concentrations. An analysis of MAF-MAF interactions based on binding studies of MAF to glutaraldehyde-fixed sponge cells and MAF-derivatized beads demonstrates that the requirement for high calcium concentrations can be overcome by extremely small amounts of certain polycations such as polybrene, polylysine, or histones. For measurements of the affinity of these substances of MAF, a method was adopted that partitions 125I-labeled MAF between dextran and polyethyleneglycol in an aqueous two-phase polymer system depending on the net charge of the complex formed. Since only polymers of positive charges affect binding and partitioning at low concentrations, large areas of interaction similar to those found in glycosaminoglycans are proposed for MAF. Through a multitude of appropriately spaced interaction sites, the rather weak selectivity of single charged sites could in such a system still provide strong enough specificities to explain species-specific cell sorting. The biological significance of naturally occurring polycations as well as extracellular calcium includes their role in cell recognition, sorting out as well as the ordered and continual streaming movements of groups of cells seen in the mesohyl of live sponges.

Animals↗
PubMed1981

Actin filament bundles in vaccinia virus infected fibroblasts.

When monolayer cultures of mouse 3T3 cells were infected with vaccinia virus, a rapid decrease of microfilament bundles was observed. The major disappearance of the cellular microfilaments occurred within the first hour after vaccinia virus infection, which is the period of uncoating of the virus core and early viral protein synthesis. The microfilament bundles of infected cells were significantly preserved in the presence of puromycin which inhibits viral protein synthesis.

Actins↗
PubMed1981

An inhibitor of animal cell growth increases cell-to-cell adhesion.

The interactions of both normal and transformed cells with their environment is mediated to a large extent by the cell surface. Succinylated concanavalin A (succinyl-Con A) is a nontoxic and nonagglutinating derivative of the jack-bean lectin concanavalin A. Succinyl-Con A, presumably through an interaction with the cell surface, reversibly inhibits the growth of normal cells and restores a normal growth phenotype to transformed cells. Whereas at high cell densities migration was inhibited, it turned out that at low cell densities where cells are not in contact with each other, cell movement was not affected by succinyl-Con A. Together with some additional observations, this suggests that this lectin derivative increases cell-to-cell adhesion in culture and thereby may influence cell migration. An increase in cell-to-cell adhesion by this lectin derivative may not be brought about simply by physically linking cells together. It occurs after a lag time, possibly by inducing surface changes. The relationship between cell adhesion in culture, cell movement, and cell growth is discussed.

Animals↗
PubMed1980

Cell-cell recognition: specific binding of Microciona sponge aggregation factor to homotypic cells and the role of calcium ions.

Previous studies have established that the mechanism of species-specific sponge cell reaggregation in vitro involves at least three components: a species-specific aggregation factor, its cell surface receptors, and Ca2+ ions. Here we report about the binding of Microciona 125I-labeled aggregation factor to cells and to other molecules of aggregation factor coupled to agarose beads, as well as the role of divalent cations in both factor-cell and factor-factor interactions. Our results indicate that cell aggregation is a two-step process, involving (1) Ca2+-independent species-specific binding of the 21 X 106 dalton aggregation factor to cellular receptors and (2) formation of Ca2+-dependent linkages between factor molecules on adjacent cells. Quantitation of binding suggests that less than 5% of the cell-associated aggregation factor in vivo is required for cell-cell adhesion in the in vitro assay. Alternative biological functions for the aggregation factor are discussed.

Animals↗
PubMed1980

Modulation of EGF binding and action by succinylated concanavalin A in fibroblast cell cultures.

The role of the binding of succinylated concanavalin A to tissue culture cells in influencing epidermal growth factor (EGF)-mediated cell proliferation has been studied. Succinylated concanavalin A dramatically reduces the stimulation of 3T6 cells by EGF in Dulbecco's modified Eagle's medium (DME) containing insulin and vitamin B12 as additional growth factors, but no serum. Furthermore, binding studies using 125I-labeled EGF have shown that the binding of EGF to the cell surface is reduced upon addition of succinylated concanavalin A.

Animals↗
PubMed1980

Hereditary motor endplate disease (med) of the mouse: observations on dissociated myogenic cells and their development in culture.

Myogenic cells from mice homozygous for the lethal mutation "motor endplate disease" (med/med) were grown in culture. Like muscle cells taken from wild type (+/?) litter mates they fused to form myotubes which contracted, developed cross striations, and exposed acetylcholine receptors (AChR) on their surface. However, a decrease of 30% in the number of mononucleated cells per unit fresh weight of muscle was observed as early as 2--3 days postnatal, i.e., at least one week prior to the onset of physiological symptoms. Hence, in addition to influencing the functional maintenance of motor endplates, the med gene seems to control early events in muscle development.

Animals↗