Tumor necrosis factor-alpha decreases thyrotropin-induced 5'-deiodinase activity in FRTL-5 thyroid cells.
Tumor necrosis factor-alpha (TNF-alpha) exerts various effects on many cell types. Acute administration of TNF-alpha to rats decrease hepatic 5'-deiodinase activity (5'D-I) and TNF-alpha has been implicated in the pathogenesis of the low triiodothyronine syndrome in non-thyroidal illness in humans. The thyroid, liver and kidney are rich in 5'D-I. Unlike hepatic and renal 5'D-I, thyroid 5'D-I is regulated by thyrotropin. We have investigated the effects of TNF-alpha on 5'D-I in FRTL-5 cells, a cultured rat thyroid follicular cell line. Tumor necrosis factor-alpha did not significantly affect basal 5'D-I but thyrotropin markedly increased 5'D-I (p < 0.001). This TSH-induced increase in 5'D-I was attenuated by TNF-alpha in a dose-dependent manner (p < 0.001). Enzyme kinetic analysis demonstrated that thyrotropin increased 5'D-I by increasing Vmax (p < 0.01) without significantly affecting Km. Likewise, TNF-alpha decreased the thyrotropin-induced 5'D-I by decreasing Vmax (p < 0.05) but not Km. The effect of TNF-alpha on thyrotropin-induced 5'D-I in FRTL-5 cells is probably mediated through post-thyrotropin-induced generation of cyclic adenosine monophosphate (cAMP) because TNF-alpha inhibited both dibutyryl cAMP (p < 0.001) and forskolin (p < 0.001)-induced increases in 5'D-I without affecting cAMP generation stimulated by thyrotropin. In conclusion, we have demonstrated that TNF-alpha inhibits thyrotropin-induced 5'D-I activity in FRTL-5 cells by pathways distal to the generation of cAMP and that TNF-alpha may play a role in the modulation of the production of triiodothyronine by the thyroid gland. (ABSTRACT TRUNCATED AT 250 WORDS)
Ongphiphadhanakul
B
B
Division of Endocrinology, University of Massachusetts Medical School, Worcester 01655.
Fang
S L
SL
Tang
K T
KT
Patwardhan
N A
NA
Braverman
L E
LE
D000818:Animals; D003994:Bucladesine / Q000037:antagonists & inhibitors; D002460:Cell Line; D005576:Colforsin / Q000037:antagonists & inhibitors; D000242:Cyclic AMP / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D007453:Iodide Peroxidase / Q000037:antagonists & inhibitors*; D051381:Rats; D013961:Thyroid Gland / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D013972:Thyrotropin / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology* / Q000502:physiology
D014409:Tumor Necrosis Factor-alpha; D005576:Colforsin; D003994:Bucladesine; D013972:Thyrotropin; D000242:Cyclic AMP; D007453:Iodide Peroxidase