The binding of the mucoprotein from gastric mucus to cells in tissue culture and the inhibition of cell adhesion

The mucoprotein, which is responsible for the formation of gastric mucous gel in pig, has been shown to bind equally well to suspensions of baby hamster kidney cells, polyoma-virus-transformed baby hamster kidney cells and HeLa cells. The binding of the mucoprotein to the cells is dependent on Ca2+/Mg2+ ions and is 5-fold greater at 37 than 4 °C. Prolonged treatment of the cells with trypsin reduces their binding capacity for the mucoprotein to less than half. The rate of adhesion of single “S-labelled baby hamster kidney cells, polyoma-transformed baby hamster kidney cells and HeLa cells to the different monolayers has been studied and found to be about the same for all 3 types of cell. The same gastric mucoprotein which bound to the cells also inhibited the adhesion of the different types of single cells to the monolayers. Thus, about one μmol l.-1 of gastric mucoprotein reduced the adhesion of single BHK cells to BHK monolayers to one-seventh of that in the absence of mucoprotein. The binding of the mucoprotein to the cells is essentially irreversible, and also single cells preincubated with the mucoprotein do not adhere to the monolayers when no free mucoprotein is present. Both the binding of the mucoprotein to the cells and its inhibitory action on cell adhesion are abolished if high concentrations of calf serum are included in the medium. Red blood cells neither adhere to each other nor do they bind the mucoprotein. The interaction of the mucoprotein with the cells is specific in that bovine serum albumin, calf serum, glycogen and hyaluronic acid neither affected the adhesion between the cells nor in the case of bovine serum albumin bound significantly. Furthermore, measurements of binding show that only a fraction of the purified mucoprotein (6%) has the necessary primary and/or tertiary structure to combine with the receptor sites on the cell surface. The similarities between the adhesion of the cells to monolayers and the binding of the gastric mucoprotein to these cells is discussed in terms of the importance of cell surface mucoproteins in cell adhesion.