Expression of the type II iodothyronine deiodinase in cultured rat astrocytes is selenium-dependent

The iodothyronine deiodinases are a family of selenoproteins that metabolize thyroxine and other thyroid hormones to active and inactive metabolites in a number of tissues including brain. Using primary cultures of rat astroglial cells as a model system, we demonstrate that the mRNA for the type II iodothyronine deiodinase (DII) selenoenzyme is rapidly and markedly induced by forskolin and 8-bromo-cAMP. The induction of DII activity, however, was significantly impaired by culturing cells in selenium-deficient medium for 7 days. Under such conditions, the addition of selenium resulted in a rapid increase in cAMP-induced DII activity that was dose-dependent, with maximal effects noted within 2 h. Cycloheximide blocked this effect of selenium on restoring cAMP-induced DII activity, whereas actinomycin D did not. These data demonstrate that the DII selenoenzyme is expressed in cultured astrocytes and that the induction of DII activity by cAMP analogues appears to be mediated, at least in part, by pretranslational mechanisms. Furthermore, selenium deprivation impairs the expression of DII activity at the level of translation.