Changes in cytosolic 3,5,3'-tri-iodo-L-thyronine (T3) binding activity during administration of L-thyroxine to thyroidectomized rats: cytosolic T3-binding protein and its activator act as intracellular regulators for nuclear T3 binding.
Changes in the amount of cytosolic 3,5,3'-tri-iodo-L-thyronine (T3)-binding protein (CTBP) and its activator during administration of L-thyroxine (T4) to thyroidectomized rats were investigated. Thyroidectomy decreased the amount of CTBP in the kidney, whereas the activator was not significantly modified by thyroidectomy. The activator was increased by administration of T4 to thyroidectomized rats. The amount of CTBP was also increased by administration of T4. The activator increased the maximal binding capacity (MBC) without changes in the affinity constant for T3 binding in CTBP. A T4-induced increase in MBC in cytosol inhibited nuclear T3 binding in vitro by competition of T3 binding between CTBP and the nuclear receptor. These results suggest that thyroid hormone increases the capacity for cytosolic T3 binding through increasing the amount of CTBP and its activator, and that these increases play a role in regulating the amount of T3 that binds to its nuclear receptor.
Nishii
Y
Y
Department of Geriatrics, Endocrinology and Metabolism, Shinshu University School of Medicine, Nagano-ken, Japan.
Hashizume
K
K
Ichikawa
K
K
Miyamoto
T
T
Suzuki
S
S
Takeda
T
T
Yamauchi
K
K
Kobayashi
M
M
Yamada
T
T
D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D003600:Cytosol / Q000378:metabolism; D007668:Kidney / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism*; D051381:Rats; D013963:Thyroid Hormones; D013965:Thyroidectomy; D013974:Thyroxine / Q000378:metabolism* / Q000494:pharmacology*; D013997:Time Factors; D014284:Triiodothyronine / Q000378:metabolism*; D000097810:Thyroid Hormone-Binding Proteins
D002352:Carrier Proteins; D008565:Membrane Proteins; D013963:Thyroid Hormones; D013974:Thyroxine; D014284:Triiodothyronine; D000097810:Thyroid Hormone-Binding Proteins