Responsiveness of glycosyltransferases to thyrotropin in a serum-free culture of porcine thyroid cells.

Administration of thyrotropin to porcine thyroid follicles, obtained in a serum-free chemically defined medium, provoked marked increases in the activities of several glycosyltransferases involved in protein N-glycosylation. The coincidence of these effects with a previously demonstrated enhancement of thyroglobulin production renders a relationship between these events likely. The most important stimulation was for peptide oligosaccharyltransferase (3-fold). Among the enzymes involved in the synthesis of the lipid oligosaccharide donor, Dol-P glycosyl- and mannosyltransferases were increased 1.5-fold, and Dol-P N-acetylglucosaminylphosphotransferase only 1.15-fold. As regards terminal glycosyltransferases, asialofetuin sialyltransferase was increased 2-fold and ovomucoid galactosyltransferase only 1.2-fold. There was a continuous release of the latter two enzymes into the culture medium.