EXPRESSION OF THE TYPE-II IODOTHYRONINE DEIODINASE IN CULTURED RAT ASTROCYTES IS SELENIUM-DEPENDENT

The iodothyronine deiodinases are a family of selenoproteins that meta bolize thyroxine and other thyroid hormones to active and inactive met abolites in a number of tissues including brain, Using primary culture s of rat astroglial cells as a model system, we demonstrate that the m RNA for the type II iodothyronine deiodinase (DIE) selenoenzyme is rap idly and markedly induced by forskolin and 8-bromo-cAMP. The induction DII activity, however, was significantly impaired by culturing cells in selenium-deficient medium for 7 days, Under such conditions, the ad dition of selenium resulted in a rapid increase in cAMP-induced DII ac tivity that was dose-dependent, with maximal effects noted within 2 h, Cycloheximide blocked this effect of selenium on restoring cAMP-induc ed DII activity, whereas actinomycin D did not. These data demonstrate that the DII selenoenzyme is expressed in cultured astrocytes and tha t the induction of DII activity by cAMP analogues appears to be mediat ed, at least in part, by pretranslational mechanisms, Furthermore, sel ensium deprivation impairs the expression of DII activity at the level of translation.