THYROTROPIN CONTROLS DOLICHOL-LINKED SUGAR POOLS AND OLIGOSACCHARYLTRANSFERASE ACTIVITY IN THYROID-CELLS

We previously showed that thyroglobulin (Tg) glycosylation is enhanced 1.5-fold under thyrotropin (TSH) stimulation, corresponding to an inc reased number of oligosaccharide chains per molecule of Tg. Now the st eps involving dolichol components and oligosaccharyltransferase activi ty have been studied. Porcine thyroid cells were cultured on porous bo ttom filters with or without TSH and incubated with [C-14]mevalonate. Under TSH regulation, the level of the whole of dolichol components wa s increased 1.25-fold without modifying their distribution. Dolichol, and free and monosaccharide-linked dolichyl-phosphate, represented res pectively 40% and 45% of total dolichol components while dolichyl-pyro phosphate-oligosaccharide represented 3% only. A marked enhancement (4 .2-fold) of oligosaccharyltransferase activity occurred in stimulated cells, which could correspond to the addition of the two TSH effects: stimulation of Tg synthesis (3-fold) and of Tg glycosylation (1.5-fold ). The amount of lipid carriers appeared to be insufficiently increase d but no component is a limiting step, suggesting that the turnover of dolichol derivatives may be increased under TSH control through their use by higher amounts of Tg.