Regulation of type II iodothyronine 5'-deiodinase by thyroid hormone. Inhibition of actin polymerization blocks enzyme inactivation in cAMP-stimulated glial cells

• Published in: The Journal of biological chemistry 1990-01, Vol.265 (2), p.940-946
• Main Authors: Leonard, J L, Siegrist-Kaiser, C A, Zuckerman, C J
• Format: Article
• Language: English
• Subjects: Actins - metabolism; Animals; Astrocytes - enzymology; Biological and medical sciences; Carbonyl Cyanide m-Chlorophenyl Hydrazone - pharmacology; Cell physiology; Cells, Cultured; Cyclic AMP - metabolism; Cycloheximide - pharmacology; Cytochalasin B - pharmacology; Dactinomycin - pharmacology; Enzyme Induction; Fundamental and applied biological sciences. Psychology; Hormonal regulation; Hydrocortisone - pharmacology; Iodide Peroxidase - biosynthesis; Iodide Peroxidase - metabolism; Molecular and cellular biology; Neuroglia - drug effects; Neuroglia - enzymology; Neuroglia - metabolism; Polymers; Rats; Thyroid Hormones - physiology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(19)40140-3

The cellular events mediating the rapid, thyroid hormone-dependent modulation of membrane-bound, type II iodothyronine 5'-deiodinase were studied in dibutyryl cyclic AMP(bt2cAMP)-treated brain astrocytes. Unstimulated cells had undetectable type II 5'-deiodinating activity. Treating the cells with bt2cAMP and hydrocortisone induced enzyme expression by increasing transcription of the enzyme or an essential enzyme related protein(s), with steady-state levels of type II 5'-deiodinase attained after 8 h of bt2cAMP treatment. Glial cells grown in the absence of thyroid hormone had 10-15-fold higher levels of 5'-deiodinating activity than cells grown in the presence of serum. The increased type II 5'-deiodinating activity observed in serum-free cultures was due to a prolonged enzyme half-life with no change in the rate of enzyme synthesis. Addition of thyroxine or 3,3',5'-triiodothyronine to the serum-free culture medium resulted in a concentration-dependent fall in steady-state enzyme levels, with EC50 values of approximately 0.4 nM. 3,5,3'-Triiodothyronine was at least 100-fold less effective. Chloroquine, NH4Cl, tunicamycin, colchicine, and monodansylcadavarine had no effect on the t1/2 of the enzyme, while both carbonyl cynanide m-chlorophenylhydrazone and cytochalasins completely blocked the inactivation of the type II 5'-deiodinase. These data indicate that in glial cells, an intact actin-cytoskeleton is required for thyroid hormone to modulate the energy-dependent regulation of the half-life of the short-lived, membrane-bound enzyme, type II 5'-deiodinase.