Effect of retinoic acid on cell surface glycopeptides of cultured spontaneously transformed mouse fibroblasts (BALB/c 3T12–3 cells)

Previous work has shown that treatment of poorly adhesive, spontaneously transformed 3T12 fibroblasts with active retinoids greatly increases their adhesion to the culture dish surface. Inasmuch as vitamin A enhances the biosynthesis of glycoproteins, we investigated whether the increased adhesion was simultaneous with an effect on incorporation of monosaccharides into glycoproteins. Gel filtration analysis of the total cellular glycopeptides showed [2-³H]mannose to be incorporated into a minor component (Fraction I) with an approximate molecular weight of 2100 and a major component (Fraction II) with an approximate molecular weight of 1500. The same [2-³H]mannose-labeled glycopeptides (Fractions I and II) were also obtained from the cell surface of 3T12 cells by short pronase treatment. [5, 6-³H]Fucose was incorporated only into Fraction I of the cell surface glycopeptides. Cell surface glycopeptides were enriched in Fraction I as compared with the total cellular material, which contained mostly Fraction II. Retinoic acid caused an increase in adhesion of the cells and a 58% increase in the amount of mannose incorporated into total cellular glycoproteins. Moreover, this retinoid caused a relative increase in the amount of mannose incorporated into cell surface Fraction I, but it did not affect appreciably the ratio of Fraction I to Fraction ll in the total cellular extract. Characterization of glycopeptides (Fractions I and II) was conducted using exo-and endoglycosidase treatment, as well as affinity chromatography on concanavalin A-Sepharose. From these studies, Fraction I was concluded to be of the “complex” type, e., of the type containing, in addition to di-N-acetylchitobiose and mannose, N-acetylglucosamine, galactose, sialic acid, and, occasionally, fucose. Fraction II was found to be of the “polymannose” type, i.e., of the type containing di-N-acetylchitobiose and a polymannose chain. It is suggested that the effect of retinoic acid on cellular adhesion may well be related to its effect on the biosynthesis of cell surface glycoconjugates.