title: 3,5,3'-triiodo-L-thyronine binding sites in nuclei of human trophoblastic cells.
abstract: Nuclear binding sites of T3 in human trophoblastic cells were biochemically characterized. Nuclei were isolated by a combination procedure with mild homogenization of the freshly obtained trophoblastic tissue aged term gestation, centrifugations and Triton X-100 treatment. The isolated nuclei were incubated with various concentrations of 125I-T3 at 20 degrees C for 3 h. The total number of T3 binding sites per nucleus was approximately 650. The apparent association constant (Ka) was 6.0 X 10(9)M-1. Nuclear proteins extracted from purified nuclei with 0.4M KCl were able to bind T3 giving rise to nuclear thyroid hormone binding protein-T3 complexes and they were precipitated with bovine IgG, as a carrier protein, by 12.5% polyethylene glycol. Binding was maximum in 3 h incubation at 20 degrees C or in 18 h at 0 degrees C, while it dropped quickly at 37 degrees C. The binding characteristics were analyzed by Scatchard plots. In nuclear proteins obtained from 8 term placentae there was a single set of high affinity-low capacity T3 binding sites with Ka of 7.0 X 10(9)M-1. The capacity is about 62.7 fmol T3/mg DNA. The binding sites were found to be specific for L-T3, while L-T4 was about 100-fold less effective, rT3 ineffective, and D-T3 and D-T4 were roughly 1/8 and 1/5 as active as L-T3 and L-T4, respectively in displacing 125I-T3 from the binding sites. These data confirmed that human placenta is a target organ of thyroid hormones; trophoblastic cells contain T3 nuclear receptors which are biochemically similar to those isolated from liver, although the capacity is low.
authors.affiliation: Department of Obstetrics and Gynecology, Kobe University School of Medicine, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Ashitaka
authors.forename: M
authors.initials: M
authors.lastname: Maruo
authors.forename: Y
authors.initials: Y
authors.lastname: Takeuchi
authors.forename: H
authors.initials: H
authors.lastname: Nakayama
authors.forename: M
authors.initials: M
authors.lastname: Mochizuki
mesh_terms: D002467:Cell Nucleus / Q000378:metabolism* / Q000648:ultrastructure; D006801:Humans; D008024:Ligands; D009687:Nuclear Proteins / Q000032:analysis / Q000302:isolation & purification; D011988:Receptors, Thyroid Hormone / Q000032:analysis; D014284:Triiodothyronine / Q000378:metabolism*; D014327:Trophoblasts / Q000166:cytology* / Q000648:ultrastructure
chemical_list: D008024:Ligands; D009687:Nuclear Proteins; D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine