12-O-tetradecanoylphorbol 13-acetate and fibroblast growth factor increase the 30-kDa substrate binding subunit of type II deiodinase in astrocytes.

Type II 5'-deiodinase (D-II) catalyzes the intracellular conversion of thyroxine (T4) to 3,5,3'-triiodothyronine (T3) in the brain. The D-II activity in astroglial cell cultures is induced by several pathways including cyclic AMP (cAMP), 12-O-tetradecanoylphorbol 13-acetate (TPA), and fibroblast growth factors (FGFs). We have examined the effect of TPA and FGFs on the 30-kDa substrate binding subunit of D-II, by affinity labeling with N-bromoacetyl-[125I]T4 in astroglial cells. TPA (0.1 microM), 20 ng/ml acidic FGF (aFGF), and 1 mM 8-bromo cyclic AMP all caused an increase in the 30-kDa protein. cAMP induced the greatest increase (fivefold) followed by TPA (3.2-fold) and FGF (2.8-fold). Glucocorticoids acted synergistically with cAMP and aFGF and promoted the effect of TPA. Affinity labeling was competitively inhibited by bromoacetyl-T4 > bromoacetyl-T3 > T4 > reverse T3 > iopanoic acid > T3 > 3,5,3'-triiodothyroacetic acid. The effect of TPA (0.1 microM) was maximum at 8 h and then gradually decreased. aFGF (20 ng/ml) plus heparin (17 micrograms/ml) induced a maximal 30-kDa increase at 8 h, which stayed stable for up to 24 h. The effect of aFGF was concentration dependent. Of the other growth factors studied, only basic FGF and platelet-derived growth factor induced small increases in the 30-kDa protein. Epidermal growth factor had little effect. In vitro labeling of cAMP, TPA, and aFGF-stimulated cell sonicates resulted in an increase in the 30-kDa protein that paralleled the increase in D-II activity.(ABSTRACT TRUNCATED AT 250 WORDS)