HORMONAL-REGULATION OF SOME STEPS OF THYROGLOBULIN SYNTHESIS AND SECRETION IN BICAMERAL CELL-CULTURE

Porcine thyroid cells were cultured for 15 days on porous bottom chamb ers with or without different mixtures of hormones added to serum-free basal medium. Assays with 10% serum were also performed for compariso n with previously published results. The effects of the hormones, part icularly insulin, TSH and hydrocortisone, were studied on total RNA co ntent, thyroglobulin mRNA level, the amount of thyroglobulin secreted into the apical medium and on glycosylation. Insulin and TSH similarly increased the total RNA content, and their effects were additive. Thy roglobulin mRNA content was increased twofold by insulin and threefold by TSH. When they were added simultaneously, the maximal level of thy roglobulin mRNA was reached, showing that TSH and insulin effects on t hyroglobulin gene expression were additive. Hydrocortisone alone did n ot modify total RNA or thyroglobulin mRNA content but the hormone ampl ified total RNA when insulin and TSH were present together. The basal level of thyroglobulin secreted into the apical medium was increased t hreefold by insulin and fourfold by TSH. The effects of these two horm ones added together appeared to be additive. Hydrocortisone had no eff ect alone or even when combined with insulin or TSH. However, when the three hormones were added together, the hormonal response was amplifi ed. TSH effect and insulin effect on the incorporation of H-3-mannose into thyroglobulin as well as on the anionic residue content of the mo lecule were additive. (C) 1994 Wiley-Liss, Inc.