title: Nuclear thyroid hormone receptors in cultured bone cells.
abstract: Thyroid hormones influence bone metabolism, but a direct interaction of triiodothyronine with nuclear T3 receptors in bone cells has not yet been reported. We investigated 125I-T3 binding to nuclei isolated from the cloned osteoblastlike rat osteosarcoma cells ROS 17/2.8. At 37 degrees C, saturable 125I-T3 binding to isolated nuclei reached equilibrium by 30 minutes and was completely displaced upon the addition of 500 nmol/L unlabeled T3. Nonsaturable binding represented about 0.5% of the radioactivity added (20% of the total binding). Thyroxine and 3,3',5'triiodothyronine competed with 125I-T3 with a 20-fold and 400-fold lower affinity than T3, respectively. Analysis of equilibrium competition experiments revealed the presence of a single class of homogeneous binding sites with an association constant of 5.0 +/- 0.3 X 10(9) mol/L-1 and a maximum nuclear binding capacity of 0.13 +/- 0.02 ng/mg DNA. A twofold increase of bone Gla protein (BGP) secretion was observed with T3 treatment suggesting that these T3 nuclear receptors are coupled with a biological response.
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001842:Bone and Bones / Q000378:metabolism*; D002135:Calcium-Binding Proteins / Q000096:biosynthesis; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003094:Collagen / Q000096:biosynthesis; D010006:Osteoblasts / Q000378:metabolism; D015675:Osteocalcin; D012516:Osteosarcoma; D051381:Rats; D011956:Receptors, Cell Surface / Q000378:metabolism*; D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine / Q000494:pharmacology
chemical_list: D002135:Calcium-Binding Proteins; D011956:Receptors, Cell Surface; D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine; D015675:Osteocalcin; D003094:Collagen