Studies on the mechanism of retinoid-induced adhesion of spontaneously transformed mouse fibroblasts.

Transformed cells (Balb/c, 3T12-3), induced to increase their adhesion to the substrate by treatment with retinoic acid, display higher incorporation of (2-(3)H)-mannose into both lipids and glycoproteins than untreated controls. Stimulation of (2-(3)H)-mannose incorporation into manno-lipids is evident 8 hr after exposing the cells to retinoic acid, and stimulation of tritiated mannose incorporation into glycoproteins occurs slightly later. SDS-PAGE of (2-(3)H)-mannose labelled glycoproteins indicates that both retinoic acid and retinol treatments stimulate the incorporation of the radiolabelled sugar into a glycoprotein with subunit MW 180,000 (Gp 180) and, to a lesser extent, into other glycoproteins. 3H-leucine incorporation into a protein banding at the same position as the 3H-mannose labelled Gp 180 does not appear to be affected by retinoid treatment. A retinoic acid induced increase in the amount of Gp 180 can also be shown by lactoperoxidase catalyzed radioiodination of cultured 3T12 cells, and controlled trypsin digestion experiments indicate that Gp 180 is a component of the cell surface. On the contrary, the increased cell adhesion to the substrate induced by retinoic acid is not accompanied, in this system, by an increase in the amount of fibronectin, as judged by iodination of the cell surface components followed by SDS-PAGE.