Capping of concanavalin A receptors and their association with microfilaments in monolayer grown human fibroblastoid cells.

The distribution of ConA binding sites on the surface of normal human fibroblastoid cells grown in monolayer culture was carefully examined. Low concentrations of ConA (between 0.5-5.0 microgram/ml) were found to induce the ConA receptors to form a single, large cap structure. High concentrations of ConA (between 50-100 microgram/ml) inhibit cap formation at temperatures above 20 degrees C. Pretreatment of the cells in the cold or with colchicine allows cap formation to occur with high concentrations of ConA. The ConA caps appear to be preferentially localized near the nucleus. Using a double immunofluorescence technique, we have observed actin and myosin molecules concentrated underneath the surface receptor cap in the perinuclear region of the cells. These findings suggest that the binding of ConA to fibroblastoid cells may trigger the transmembrane association of cytoplasmic microfilaments with surface membrane receptors as previously proposed for lymphocytes and other round cells grown in suspension culture.