Synergistic effect of thyroid hormone and thyrotropin on iodothyronine 5'-deiodinase in FRTL-5 rat thyroid cells.
The effects of T3 and T4 on the iodothyronine 5'-deiodinase (5'-D) activity in FRTL-5 rat thyroid cells were investigated. T3 and T4 stimulated the 5'-D activity in a dose-dependent manner. Kinetic studies showed that the stimulation of the 5'-D by T3 was associated with an increase in maximum velocity (Vmax) in [11.9 +/- 0.2 (mean +/- SE) and 25.4 +/- 0.9 pmol I-released/mg protein.min, respectively, in control and cultured with 10(-9) M T3 for four days] but without a change in apparent Michaelis-Menten constant (Km) (94.8 +/- 5.3 nM and 105.4 +/- 12.1 nM, respectively). Furthermore, cycloheximide (5 microM) completely abolished the stimulatory effect of T3 on the 5'-D activity. T3 and T4 also enhanced the 5'-D activity stimulated by TSH in a dose-dependent manner. Kinetic studies showed that the stimulatory effect of T3 on the 5'-D stimulated by TSH was again associated with an increase in Vmax (86.0 +/- 4.0 and 166.5 +/- 1.9 pmol I- released/mg protein.min, respectively, cultured with 0.3 U/liter TSH and cultured with TSH plus 10(-9) M T3 for four days) without a change in apparent Km (114.0 +/- 7.4 nM and 111.6 +/- 12.5 nM, respectively). Cycloheximide (5 microM) completely abolished the stimulatory effect of TSH plus T3 on the 5'-D activity. There were no significant differences observed between cells cultured with TSH and with TSH plus T3 in either the intra- or extracellular cAMP contents. Furthermore, T3 enhanced the 5'-D activity stimulated by (Bu)2 cAMP. These results strongly suggest that T3 or T4 was synergistic with TSH in stimulating the 5'-D activity in FRTL-5 cells, and that cAMP production would be an important component of the synergism.
Toyoda
N
N
Second Department of Internal Medicine, Kansai Medical University, Osaka, Japan.
Nishikawa
M
M
Horimoto
M
M
Yoshikawa
N
N
Mori
Y
Y
Yoshimura
M
M
Masaki
H
H
Tanaka
K
K
Inada
M
M
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002460:Cell Line; D000242:Cyclic AMP / Q000096:biosynthesis; D003513:Cycloheximide / Q000494:pharmacology; D004357:Drug Synergism; D007453:Iodide Peroxidase / Q000378:metabolism*; D007454:Iodides / Q000378:metabolism; D007700:Kinetics; D051381:Rats; D013961:Thyroid Gland / Q000187:drug effects / Q000201:enzymology*; D013972:Thyrotropin / Q000494:pharmacology*; D013974:Thyroxine / Q000494:pharmacology*; D014284:Triiodothyronine / Q000494:pharmacology*
D007454:Iodides; D014284:Triiodothyronine; D003994:Bucladesine; D013972:Thyrotropin; D003513:Cycloheximide; D000242:Cyclic AMP; D007453:Iodide Peroxidase; D013974:Thyroxine