Correlation of retinoic acid-enhanced sialyltransferase activity and glycosylation of specific cell surface sialoglycoproteins with growth inhibition in a murine melanoma cell system

Retinoic acid inhibits the proliferation of the murine melanoma clone S91-C-2 cells, enhances the glycosylation of specific cell surface sialoglycoproteins, and stimulates sialytransferase activity. Mutant clones, selected from the S91-C-2 cells for resistance to the growth-inhibitory effect of retinoic acid, were used to explore whether cell surface modulation by retinoic acid is related to growth inhibition. Glycoprotein synthesis was assessed by analysis of [3H]glucosamine incorporation into glycoconjugates, and cell surface sialo- and galactoglycoproteins were analyzed after radiolabeling by the NaIO4:NaB3H4 and the neuraminidase plus galactose oxidase:NaB3H4 methods, respectively. The cells were solubilized and the labeled molecules were separated by polyacrylamide gel electrophoresis and identified by fluorography. Sialytransferase activity was measured in detergent-solubilized cells, using cytidine 5' -monophosphate-[14C]sialic acid as a sugar donor and asialofetuin as an exogenous acceptor. The results demonstrated that retinoic acid enhanced [3H]glucosamine incorporation into a Mr 160,000 glycoprotein in the S91-C-2 cells but not in any of the resistant mutant clones, while the pattern of [35S]methionine-labeled proteins was not modified in either the sensitive or the resistant clones. Radiolabeling of a Mr 160,000 sialoglycoprotein on the surface of S91-C-2 and of several retinoic acid-sensitive subclones of S91-C-2 was augmented by retinoic acid. A considerably smaller effect was observed on the labeling of Mr 160,000 sialoglycoprotein on one of the resistant clones, and no significant effect could be detected on the other resistant mutant clones. Sialytransferase activity was increased 2- to 3-fold by retinoic acid in the S91-C-2 cells and in several sensitive subclones, but not in any of the resistant mutant clones. Tetradecanoylphorbol acetate, which inhibits the proliferation of both retinoic acid-sensitive and retinoic acid-resistant cells, failed to increase either sialyltransferase activity or cell surface labeling of sialoglycoproteins. These findings suggest that the ability of retinoic acid to stimulate sialyltransferase activity and glycosylation of cell surface glycoproteins is related to the growth-inhibitory effect of this compound.