Inhibitory effect of thyrotropic hormone on apoptosis induced by actinomycin D in a functioning rat thyroid cell line

Apoptosis appears to play important roles in physiological and pathological processes in the endocrine system including the thyroid, but little is known about the regulation of apoptosis in the thyroid. The functioning rat thyroid cell line (FRTL-5), a cloned cell line of differentiated thyroid cells, hardly undergoes apoptosis. In this study we examined the factors which prevent FRTL-5 cells from undergoing apoptosis. After culturing FRTL-5 cells in medium with and without TSH, actinomycin D (AMD) or cycloheximide (CHX) was added. CHX did not induce apoptosis. AMD induced apoptosis in FRTL-5 cells cultured in medium lacking TSH, as confirmed by the presence of DNA fragmentation, together with nuclear fragmentation and condensation, but AMD did not induce apoptosis in FRTL-5 cells cultured in the presence of TSH. Furthermore, the fact that AMD did not induce apoptosis in FRTL-5 cells cultured with dibutyryl cyclic AMP (Bt2cAMP), or forskolin suggests that TSH has an inhibitory effect on apoptosis in FRTL-5 cells via the TSH-cAMP pathway.