An evaluation of the role of gangliosides as receptors for fibronectin.

The demonstration that exogenous gangliosides, in particular the di- and tri-sialogangliosides can inhibit fibronectin-mediated cell adhesion led to the proposal that these molecules may act as cell surface receptors for fibronectin. I have attempted to make a detailed evaluation of this proposal by taking the following approaches. 1. Making a more extensive study of the ability of gangliosides to inhibit cell adhesion, in particular cell spreading, in order to determine whether or not this activity is specific for fibronectin. 2. Attempting to demonstrate a direct interaction between fibronectin and gangliosides adsorbed to a plastic support. This involved the use of either 125I-labelled fibronectin or a sensitive radioimmune detection system. 3. Investigating whether a cell surface ganglioside is capable of supporting stable cell adhesion by analysing cell spreading on substrata coated with cholera toxin, a ganglioside-binding ligand. Cholera toxin- induced cell spreading is compared with that on fibronectin and the glycoprotein reactive lectin concanavalin A in an attempt to assess the relative importance of glycoproteins and gangliosides in mediating fibronectin-induced cell spreading. 4. Finally I have investigated the relationship between the levels of cellular gangliosides and the ability to interact with fibronectin. This involved: - (i), a comparison of the ability of Balb/c 3T3 cells and four ganglioside-deficient variant cell lines to interact with FN, (ii), investigating the effect of adding back exogenous gangliosides to a cell line lacking gangliosides on its ability to retain fibronectin at the cell surface, and (iii), conversion of cellular di- and tri-sialogangliosides into monosialogangliosides by neuraminidase treatment and examining the cell's ability to spread on fibronectin-coated substrata. In general this data is not consistent with the proposal that gangliosides act as the sole receptor for fibronectin.