Cyclic adenosine 3',5'-monophosphate and glucose stimulate thyroxine 5'-deiodinase type II in cultured mouse neuroblastoma cells.

Nutrient modulation increases mouse neuroblastoma (NB) T4-5'-deiodinase II (T4-5'-D II) activity. Carbohydrates are more potent than either amino acids or glycerol as nutrient sources. Glucose rapidly (2 to 4 hours) enhances NB enzyme activity and the response is dependent on new protein synthesis. The present study was performed to further characterize this glucose effect and explore its relationship to the cyclic adenosine monophosphate (cAMP) system in these cells. NB T4-5'-D II activity reached a maximum level (sixfold) in response to glucose (10 mmol/L) at 16 hours and thereafter remained constant up to 22 hours before reverting back to basal level between 24 and 30 hours. This pattern of response allowed the performance of detailed studies on maximum glucose activated NB T4-5'-D II under transient equilibrium conditions during the 16- to 22-hour period. Addition of dibutyryl cAMP (dbcAMP) (1 mmol/L) at this stage significantly increased enzyme activity (twofold at 2 hours and fourfold at 4 and 6 hours) compared with glucose alone. There was an additive response to dbcAMP under these maximum glucose-activated conditions. Nonactivated NB T4-5'-D II showed a twofold response to dbcAMP (1 mmol/L) at 4 hours in a glucose-free medium. Under these conditions, glucose (10 mmol/L) also increased enzyme activity twofold. Combined studies with dbcAMP and glucose increased enzyme activity fourfold at 4 hours. Subsequent studies were performed with forskolin (10 mumol/L) and cholera toxin (1 nmol/L), modulators of endogenous cAMP.(ABSTRACT TRUNCATED AT 250 WORDS)