Glycopeptide alterations induced by 12-O-tetradecanoyl phorbol-13-acetate in chick embryo cultured myotubes.

The tumor promoter 12-O-tetradecanoyl phorbol-13-acetate (TPA) specifically inhibits the expression of differentiative traits in cultured chick embryo myotubes, without inducing them to reenter the cell cycle. We evaluated the effect of TPA on glycoconjugate synthesis in cultured myotubes under various experimental conditions. Radioactively labelled glycoconjugates were obtained by labelling control and TPA treated cultured myotubes with radioactive monosaccharides. After chloroform-methanol extraction and extensive pronase digestion, the glycoconjugates were separated on the basis of size on Sephadex G 50 columns. A relative enrichment in larger glycopeptides was induced by TPA treatment of myotubes for 24 or 48 h. Glycopeptide groups were further analyzed by affinity chromatography on ConA Sepharose columns. A marked and reproducible decrease in the affinity of medium size glycopeptides for ConA was observed as a result of TPA treatment of cultured myotubes. These modifications are reversible upon removal of the tumor promoter from the culture medium of pretreated myotubes. The reported effects of TPA, closely resembling those occurring in transformed cells, appear to be due to structural modifications of glycopeptides whose mechanism and role in transformation and modulation of differentiation are discussed.