Thyrotrophin and cyclic AMP regulation of thyroglobulin gene expression in cultured porcine thyroid cells

The effects of thyrotrophin, cholera toxin and 8-chloro-cyclic AMP on thyroglobulin gene expression in cultured porcine thyroid cells were compared. Cells organized either into monolayers in culture chambers with porous bases or into inside-out follicles in suspension were used. Thyroglobulin mRNA content was measured by dot-blot hybridization, and thyroglobulin synthesis rate was determined by immunoprecipitation of [35S]thyroglobulin after 2 h labelling with [35S]methionine. Cholera toxin and 8-chloro-cyclic AMP increased the thyroglobulin mRNA content and thyroglobulin synthesis rate in the same ratio (approximately 3) as did thyrotrophin, showing that cyclic AMP mediates the effect of thyrotrophin on thyroglobulin gene expression. The culture chamber system provides for contact of the effectors with either the apical or the basolateral membrane. The addition of 0.02-0.1 mU thyrotrophin/ml on the basolateral side of the cell layer gave a maximal response whereas this response was not reached on the apical side even with the addition of 5 mU/ml. In contrast, cholera toxin and 8-chloro-cyclic AMP stimulated thyroid cells equally on both sides.