Triiodothyronine is required for the stimulation of type II 5′-deiodinase mRNA in rat brown adipocytes

Type II 5′-iodothyronine deiodinase (D2), produces triiodothyronine (T3) and is stimulated by cold exposure via norepinephrine (NE) release in brown adipose tissue. Cultured rat brown adipocytes require T3for the adrenergic stimulation of D2 activity. D2 mRNA expression in cultured brown adipocytes is undetectable with the use of basal conditions or NE without T3. Full D2 expression is achieved using NE + T3, especially after prolonged T3 exposure. β3-Adrenergic agonists mimic the NE action, whereas cAMP analogs do not. Prolonged exposure to T3 alone increases D2 mRNA. High T3 doses (500 nM) inhibit the adrenergic stimulation of D2 activity while increasing D2 mRNA. The effects obtained with NE + T3 or T3 alone are suppressed by actinomycin, but not by cycloheximide, which leads to accumulation of short D2 mRNA transcripts. Prolonged or short exposure to T3 did not change D2 mRNA half-life, but T3 seemed to elongate it. In conclusion, T3 is an absolute requirement for the adrenergic stimulation of D2 mRNA...