RETINOIDS STIMULATE TYPE-I IODOTHYRONINE 5'-DEIODINASE ACTIVITY IN HUMAN FOLLICULAR THYROID-CARCINOMA CELL-LINES

Iodothyronine 5'-deiodinase isoenzymes generate the thyroid hormone 3,3',5-triiodothyronine from the prohormone L-T-4 Basal and retinoic acid (RA)-induced type I 5'-deiodinase (5'DI) activities were studied in human thyroid carcinoma cell lines. In the follicular thyroid carcinoma line FTC-133, nanomolar concentrations of 9-cis-, 13-cis-, and all-trans-RA induced 5'DI activity. Kinetics with all-trans-RA revealed 5'DI stimulation after 1 day and a maximal effect after 3 days. Increased abundance of the p27 5'DI subunit was demonstrated after RA treatment by N-bromoacetyl-[I-125]T-4 affinity labeling. Actinomycin-D and cycloheximide blocked RA-mediated induction. RA stimulated 5'DI activity to a lesser extent in FTC-238 cells, whereas neither basal 5'DI activity nor stimulation by RA was found in anaplastic thyroid carcinoma, human lung, or leukemia cell lines. Steady state messenger ribonucleic acid levels of RA receptor-alpha and -beta were increased after incubation of FTC-133 cells with all-trans-RA. The high 5'DI activity of differentiated rat thyroid FRTL-5 cells was not further induced by RA. Butyrate did not alter 5'DI, but increased the activity of the differentiation marker alkaline phosphatase in FTC-133 and FTC-238 cells. T-4 and T-3 had no effect on basal or RA-stimulated 5'DI activity. These data suggest that expression and retinoid induction of 5'DI may serve as a sensitive and functional differentiation parameter of follicular thyroid carcinoma cells.