Glycolipids: Receptors for fibronectin?

Abstract

We have examined the hypothesis that glycolipids might serve as receptors for the cell surface glycoprotein fibronectin using three different biological assay systems. We find that purified solubilized gangliosides inhibit fibronectin-mediated hemagglutination, cell spreading, and restoration of a normal morphologic phenotype to transformed cells. The inhibition is dose-dependent and competitive; hemagglutination by 2 micrograms/ml fibronectin is half-maximally inhibited by less than 1 microM gangliosides. The most effective ganglioside inhibitors generally contain the most sialic acid residues. The isolated oligosaccharide portions of gangliosides retain this inhibitory activity and the oligosaccharides with more sialic acid are more effective inhibitors. A series of other lipids or ganglioside constituents are either less effective or without detectable activity. The more active of these lipids are the more negatively charged phospholipids such as phosphatidyl serine and phosphatidyl inositol. Our results support the hypothesis that the "receptors" for fibronectin on the cell surface either consist of or contain gangliosides or other negatively charged lipids.

Disialoganglioside GD2 distributes preferentially into substrate-associated microprocesses on human melanoma cells during their attachment to fibronectin.

“…We also demonstrated that pretreatmerit of human melanoma cells with either anti-GD2 or anti-GD3 Mabs inhibited their ability to attach to a number of extracellular matrix proteins (10). These data are in support of the studies that implicate gangliosides in cell-substratum interactions (18,29,49). The conclusion reached in these reports were based upon the exogenous addition of gangliosides to cultured cells under the assumption that the exogenously added gangliosides could embed appropriately in the plasma membrane of the cells being examined.…”

“…A number of reports have indicated that the exogenous addition of polysialogangliosides to fibronectin-attached cells caused them to round up and detach from the substrate (18,29,49). These studies led to the conclusion that gangliosides may act as specific fibronectin receptors.…”

“…Direct evidence is provided that GD2 is involved in M21 cell attachment to fibronectin, since treatment of these cells with anti-GD2 monoclonal antibodies causes cell rounding and detachment from a fibronectin substrate. Moreover, scanning electron microscopy demonstrates that this loss of attachment of fibronectin is characterized by a perturbation of the cell attachment-promoting microprocesses that in the presence of these antibodies lose contact with the fibronectin substrate.umber of studies have indicated that the carbohydrate moiety of gangliosides plays a direct role in cellsubstratum interactions, thus implicating them as putative cell surface receptors for fibronectin and collagen (8,18,29,49). In a previous paper, we used monoclonal antibodies (Mabs) ~ that specifically recognize carbohydrate determinants on the gangliosides GD2 and GD32 (8) to localize them on the surface of human melanoma cells and their focal adhesion plaques.…”

Effects of exogenous ganglioside GM1 on different stages of cell spreading studied by directly quantifying spreading rate

“…Cell-surface gangliosides have been regarded as receptors for FN (Yamada et al, 1981;Perkins et al, 1982;Matyas et al, 1986). In this study, exogenous GM1 was potentially able to inhibit the interaction between FN and cell-surface GM1 by taking over the GM1-binding sites of substrate-coating FN or plasma FN in FCS.…”

“…(Yamada et al, 1981;Perkins et al, 1982;Matyas et al, 1986) as obviously shown in the morphological images (Figure 4). By calculating the percentage of spread cells, we found that GM1 significantly inhibited the spreading of HUVECs on FN-coated coverslips in medium supplemented with or without 0.5% FCS (but not 10% FCS) only at 0.5 h compared with the GM1-free control ( Figure 5A).…”